The business of mind storage became a profitable one, after the discovery of a magical process that allows the memories and personality of a living being to be transferred into another body. Consciousnesses are stashed in animals (or rented humans, for the wealthy) while the body undergoes surgery. Dangerous prisoners suddenly become much easier to take care of. Falconry becomes an extremely popular hobby, although in a rather altered form. The process is easy and cheap, only requiring a trained mage to do it. While in another body, one is fully capable of controlling and using the host body as if it were one's own.

For the purposes of this question:

  • Any vertebrate is capable of holding one human mind for an unlimited amount of time.

  • Intelligence is not affected by one's current body, only by the original.

  • If the host dies, the mind stored in it is lost.

  • This takes place on modern day Earth.

  • The host's mind does not exist while another mind is using that body.

My question: Based on affordability, portability, safety, and other factors, what animal is overall the best option for a mind storage business (primarily for hospital patients with painful conditions)? For example, mice would probably not be a good choice, because they have a short lifespan and could be too risky to use.

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    $\begingroup$ Seems like people we like would get interesting and fun animals ("Mom, be a Zebra while they rebuild your hip and knees!"), while people we don't like would be lobsters and snails and eels and the like ("Look at my terrarium full of internet trolls turned into angry cockroaches!") $\endgroup$ – user535733 Feb 24 at 16:00
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    $\begingroup$ The animals are kept in facilities specifically for that purpose, which are generally much nicer than a standard dog pound. These are staffed with some trained mages in case of emergency, and other staff to take care of the animals. As for communication, most of the mages are able to telepathically communicate with the clients, but there would also be a simple, universal system of signals- something like one stomp for yes, two stomps for no, one stomp with each foreleg and then nod your head for I'm-a-human-please-spare-me. $\endgroup$ – Rivershard Feb 24 at 16:10
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    $\begingroup$ @user535733 turning an internet troll into a cockroach would be a step up for them. $\endgroup$ – Justin Thyme the Second Feb 24 at 17:13
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    $\begingroup$ How bout cat, I heard they have nin... [I saw a cat approach, keyboard over head quick] $\endgroup$ – user6760 Feb 25 at 12:03
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    $\begingroup$ What happens if the original body (the mind source) dies? Does the mind die as well and host gets it's own mind back then? The host dies as well? The host becomes the only body for the mind but mind's capabilities become limited to those of host's? $\endgroup$ – Ister Feb 25 at 15:58

«primarily for hospital patients with painful conditions»

Assuming they are going to recover.

Turtles. Very sturdy, easy and cheap to keep, long-lived. You can also reduce their metabolism and keep them lethargic.

Otherwise, dogs. Not so cheap, and require way more space. At the same time, they're more active and could supply more enjoyable experiences.

In the long run, however, probably the law would start including sentences to "temporary obliteration" (i.e. involuntary hosting) for those crimes where rehabilitation is either unlikely or pointless. In those cases, criminals would be sentenced to a certain period of time during which their bodies would be occupied by someone else. Since the new occupant is a productive member of society, and the criminal is, to all intents and purposes, nowhere, less prisons are needed. So, another possibility becomes «humans».

This opens other interesting problems though: what if the new occupant damages the body? Or even modifies it - "Hey, I got two years for embezzlement, I expected to find myself aged two years, not tattooed over!". What if the new body enters a relationship? Involuntary hosts probably will require some visual identification, unless they're confined to the hospital or dedicated towns.

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    $\begingroup$ People love dogs and dogs love people. A dog would be an excellent choice, especially since they are often allowed where humans are allowed and can thus spend time with family. Humans are also quite good at understanding dogs' body language. I'd feel sorry for the poor pupper who doesn't get to live its life during that period though. They are so full of love and taking their lifetime away from them so that humans can inhabit their bodies is too sad to think about. $\endgroup$ – Kapten-N Feb 25 at 9:25
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    $\begingroup$ If microscopic animals are valid, the tardigrade may be a good contender to the turtle. They are incredibly resilient. And while they only live for a few months, they have been known to dehydrate themselves for over a decade without dying. By comparison, turtles are still prone to die due to unforeseen circumstances (e.g. a cupboard falling over). $\endgroup$ – Flater Feb 25 at 14:06

As much as there might be a trade in recreationally adopting the form of a golden eagle or a porpoise. A very safe and efishent storage vessle would be the goldfish:

enter image description here

Wikipedia 2019 CCSAL- Licence

Lifespan 5-10 years, small and easy to feed and house, cheap to replace when obsolete.

In a cash-strapped society this would be suitable for low value citizens, welfare-state cases or prisoners.

African Grey Parrot.

When the economy permits.:

enter image description here

Wikipedia 2019 CCSAA Licence

With a 40 to 60 year lifespan and the ability to communicate in recognisable human speach (not to mention fly) this would be a great option.

The better off citizens would I'm sure be given the choice of their preferred animal from among a suite available at each medical facility.

Ultimatley, the law of supply and demand will allow people to become whatever they want. There might be some illegal options such as an adult mayfly (too short a lifespan) or a planarians (people would be able to infinitely clone themselves and their memories at will) but commerce will prevail, it always does.

Commercial concerns.

Where commerce is concerned, fads and fashions will I'm sure come and go, the fallback option in times of financial chrisis will be the expedient and cheapest - the old goldfish.


Hospital administrators could find that there developes an illicit trade in revenge-consciousness transfers - "Do you know someone you'd like to see as a cockroach dancing on a hot tin-lid? We have the answer."

Society would then, of course need to cope with the illicit trade in body upgrades and people turning up at police stations claiming to be someone else. Interesting issues your world throws up.

  • $\begingroup$ Errr.... I thought the question is about "vertebrate" alone? $\endgroup$ – Nam Nguyen Hoang Feb 25 at 9:13
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    $\begingroup$ @NamNguyenHoang Oops, I didn't notice that. I suppose that I could change caterpillar to goldfish or some such. $\endgroup$ – Agrajag Feb 25 at 9:15
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    $\begingroup$ Swap the roaches to mice or something thought of as degrading too, while you're at it $\endgroup$ – Nam Nguyen Hoang Feb 25 at 9:17
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    $\begingroup$ ...e-fish-ent storage vessel, hahaha. Very nicely done! $\endgroup$ – Megha Feb 26 at 20:41


The pig anatomy is very close to our own. Even the pig nervous system and brain structures are very close to human. Pigs even have a similar social structure.

So it would be a short acclimatization period for the human 'mind' to adjust to the new surroundings and body.

The biggest relearning curve would be walking on four legs vs two.

The drawback is the shorter life span of the pig - 15 to 20 years potential.

  • $\begingroup$ 15 years is plenty, you could even regrow organs for a diseased body in that timespan. The main problem I see is, who would want to live as a pig? $\endgroup$ – MSalters Feb 25 at 18:19
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    $\begingroup$ @MSalters Pigs get a bum rap. They are very social around humans make great pets, and are highly intelligent. I suggest you try living in/as a pig before you critique it. Incidentally, pigs are one of the cleanest animals around. They can be house trained quite quickly. Their reputation of wanting to live in a 'pig sty' is a particularly human concoction. $\endgroup$ – Justin Thyme the Second Feb 25 at 18:25
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    $\begingroup$ Don't forget the fun pub fact that pigs experience an orgasm for up to 30 minutes. $\endgroup$ – TafT Feb 26 at 10:19

There isn't one answer, because you are applying the idea to different situations.


Used as punishment, you want something that's easy to handle, not dangerous and having big troubles running away. So something small, harmless and slow is best. Snails are out (not vertebrates), but there are also really small frogs, or of course, fish. Fish are generally easy to keep and can't run away due to lack of legs. Aquarium, done. You want to pick a species with a life expectancy higher than the prison sentence, or change bodies every few years.


Completely different requirements. You need something that is comfortable for the patient for a limited time. My best idea is cats. They sleep a lot (about 16 hours a day) but when they're awake, from what I see they are having fun, they are quite sturdy for their size and can reach places and do things that neither humans nor most other animals can. However, that would only be your default offer, because patients would most likely want a choice. Many people will want to fly, so you'll probably have some birds on offer as well as flying lessons.


How has no one said ape or chimpanzee yet? They're the animals already most similar to humans.

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    $\begingroup$ Hi Will, welcome to Worldbuilding. This kind of reply is best suited to commenting rather than an answer. Although, if I remember correctly you may not be able to comment since you're new... $\endgroup$ – Arkenstein XII Feb 25 at 3:29
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    $\begingroup$ @ArkensteinXII I disagree. This is an answer. It concretely answers the question, and gives one reason to explain itself. This is not suitable for a comment, as answers should not be posted in the form of comments. Now, you may argue that this answer is too short or needs more reasoning, and that is another story. However, this is indeed an answer, not a comment. $\endgroup$ – Revetahw Feb 25 at 8:26
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    $\begingroup$ @Will - I agree that apes could be a good idea but for a complete answer I think you need to say why similarity to human beings is an important factor. I'm sure there are many reasons but to judge the correctness of your answer we need to be persuaded. $\endgroup$ – chasly from UK Feb 25 at 10:35
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    $\begingroup$ @chaslyfromUK That is a reason to not upvote the answer, not a reason to convert it to a comment. $\endgroup$ – Yakk Feb 26 at 5:21
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    $\begingroup$ @Yakk - I actually don't get what you mean. This is a new user and I was trying to explain something about how things work here. I reckon this answer would get more upvotes if reasons were given rather than a simple statement. $\endgroup$ – chasly from UK Feb 26 at 9:22

Mantis Shrimp, for the wealthy

Although the idea of being a shrimp seems weird, the experience will surely be worthwhile, and should keep them entertained for the duration of their habitation.

Being a Mantis Shrimp would be cool for a couple reasons:

  • The claws of certain species can accelerate to 83 km/h, and hit with an impact of 1500 N. This is so fast and powerful even the shock waves can kill prey, and the claw itself can destroy aquarium glass in some species.
  • They have the most advanced natural visual system that we know of, anywhere. Some species of 16 different color preceptors, meaning that you would need to mix 16 primary colors to simulate colors accurately for them. From their point of view, we have a severe decatotritotan form of color blindness. This means that they perceive qualitatively more colors than humans. Their vision also extends into infrared and ultraviolet. They also see all qualities of polarization, whereas we see none (except linear polarization very slightly). Finally, their eyes can point in any two directions, and each have individual depth perception.
  • To go along with the last point, their bodies can produce color willfully, being able to produce nearly any color they can see. 16 dimensional color vision and color production would surely be a boon for artists!

So, I think being a mantis shrimp would be rather fun.

  • $\begingroup$ Shrimp are invertebrate though, right? $\endgroup$ – npostavs Feb 25 at 14:05
  • $\begingroup$ @npostavs: Correct. Vertebrates include fish, birds, amphibians, reptiles and mammals. Shrimp are more related to lobsters. $\endgroup$ – MSalters Feb 25 at 18:27
  • $\begingroup$ Interestingly, it seems mantis shrimp don't use their color receptors the same way we do. Instead of comparing the inputs of their different color receptors to infer a color, it seems each receptor recognizes a specific color. Meaning they don't actually see more colors than we do, but the colors they do see they process faster. nature.com/news/… $\endgroup$ – Oosaka Feb 27 at 22:39
  • $\begingroup$ @npostavs oh, whoops $\endgroup$ – PyRulez Feb 27 at 22:41
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    $\begingroup$ @PyRulez: You seem to be confusing "discriminating frequencies" with "discriminating neighboring frequencies". Being able to tell red+green from yellow is "being able to better discriminate frequencies". True, the study only looked at neighboring frequencies, but I didn't say they did a comprehensive survey of what frequencies mantis shrimp discriminate or not. They predicted, from how we know the "use primary cones to generate color" process works, what neighboring frequencies mantis shrimp should be able to discriminate, and the fact they couldn't shows they use a different process. $\endgroup$ – Oosaka Feb 28 at 9:43


While you said “Any vertebrate is capable of holding one human mind for an unlimited amount of time”, you did not specify if non-vertebrate is capable of hosting human mind. If the mind transfer process applies to all animals, and if size doesn't matter, I'd suggest Tardigrade as a good choice.

Tardigrade is known to have cyptobiosis, namely they can suspend their metabolism. They can survive under extreme environments that would kill almost any other animal.

(mostly from wiki)

  • Low temperature: few to days at 73K, few minutes at 1K.
  • High temperature: few minutes at 151°C.
  • Extreme pressure: vaccum of open space and solar radiation combined for at least 10 days, or more than 1200 Atm.
  • Dehydration: survive 10 years of dry state.
  • Radiation: Tardigrades can withstand 1,000 times more radiation than other animals.

While their average life span is only a few month, they can be dehydrated to skip a rather long time period; and the fact that they are "immune" to most fatal factors for other animals, I find it suitable for a 'storage' for human mind, especially for those who just want to stay safe and wait until their operations end.


You have opened a serious can of worms:

Scenario 1: Driver is responsible for someone else becoming a quadriplegic. Judge sentences him to a body swap.

  • Criminal => Turtle
  • Victim => Criminal's Body
  • Turtle -> Victim's body.

Scenario 2: Reconditioning. Hate working out at the gym? Have you let your self go to hell? Pay someone to swap bodies with you. They are really good at will power. In a more serious vein this may be a treatment for anorexics.

Scenario 3: You're young, and rich. You want to engage in all the sins of adulthood, but you're still underage. Swap for money into an 21 year old, and go out and party!

Scenario 4: Kidnap someone. Mind swap. You in their body commits serious crimes. Come back. Swap back. You get off scot free.

Scenario 5: Body napping. I'm rich, old, and ruthless. I kidnap someone young and fit, move his mind into a turtle, move into his mind, and abandon my husk.

In general: How do you prove your identity? Your present identity can be done with what you know. How do you prove that you "weren't home" when that body did a crime?


All these animals don't have the mental capacity to accommodate human consciousness that's approximately 2 petabytes. Hence prisoners, robots and cloned human bodies are the only compatible answers for this question


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