Every time one arm is cut off, two more grow in its place. The two new grown arms have 70% of the strength of the previous original arm and 100% of the control and dexterity. It's just that the arms grow indefinitely, the more they are cut the more they split.... Theoretically one could have a 100 toothpick thin arms.

If the arm is cut at the shoulder blade, it splits into two shoulder blades, if it's cut at the shoulder socket, a new socket which can accomodate for two arms grows in its place and if the arm is cut below the shoulder it will just be one arm that splits into two like the blue monkeys from the movie Avatar... That one with the sexy aliens not the one with the twinkletoes.

In case of too many arms, how does one deal with the problem? Maybe 3 or 4 are cool, but 12...well good luck sleeping or doing anything really.

Is there any way to block the growth that doesn't involve big brains and highly developed medicine?

  • 1
    $\begingroup$ What is the outcome you want from this? Killing the arm-hydra creature would definitely stop new arms from growing and any existing arms from getting in the way. Or do you want to protect from losing arms? It's not too complex, I think - I've personally lost zero arms so far without even trying hard. $\endgroup$
    – VLAZ
    Jan 13, 2021 at 13:09
  • $\begingroup$ Mass unchanged, surface area increases exponentially... problematic. $\endgroup$
    – user6760
    Jan 13, 2021 at 13:18
  • 2
    $\begingroup$ Obviously stop cutting arms off! $\endgroup$
    – Slarty
    Jan 13, 2021 at 15:42
  • 1
    $\begingroup$ Obligatory Order of the Stick giantitp.com/comics/oots0326.html $\endgroup$ Jan 16, 2021 at 0:50
  • 1
    $\begingroup$ Boy oh boy, will you love Greek Mythology. Presenting The Hecatoncheires. $\endgroup$
    – Joe Bloggs
    Jan 16, 2021 at 7:44

4 Answers 4


You mention that 2 arms grow only when an arm is cut.

An obvious solution seems therefore to constrain one of the 2 arms after the cut, so that it becomes atrophic and leaves more space to the other, free, arm.

An atrophic limb reduces basically to just something more than its bones.


You don't.

I propose a frame change, in that not having anything to stop the multi-arm situation is not a bad thing!

Obviously anything that manages to lose that many arms is unfit to live! Based on the second half of your question regarding big brains and medical tech, I'm assuming these guys are supposed to be cavemen/primitive, but sentient. If so, there'd be a lot of cultural stigma in having too many arms. A tribe or culture may have coming-of-age rituals where arms are removed (you are a man now, you need 6 arms to join the raiding party/you are a woman now, you need 8 arms to carry children etc.) but eventually having like 20 arms (or whatever arbitrary number you settle on) only shows that you keep getting your arm hacked off. Your limbs aren't effective for much of anything, and you obviously aren't smart/skilled/lucky enough to avoid serious injury. At that point your creature is just like a cripple in primitive societies. The society might try to take care of them if they've got some special rank (priestess, or old war hero for instance) but generally speaking they're on their own and quickly dead.

On the other hand, having an egregious number of arms could be a sexual signaler. Like how males of certain bird species are colorful with un-aerodynamic showoff feathers which signal to potential mates "Look how inefficient I am, I must have wildly good genes to still be able to survive." So your creature might see many-limbed creatures as "sexy" because hey, they got their arm chopped off 15 times and managed to live and regrow all those arms. They must have something genetically that makes them superior! At some point of course this runs into your 100-toothpicks argument and the thing can't support itself. But if sexual selection has taught us anything it's that said markers of sexual fitness can end up being hugely detrimental to the individual and yet somehow the species soldiers on.


Give yourself a loophole

The usual one is fire. Either you use a red hot blade to remove a limb, pour tar into the wound, or just shove a burning branch in the hole. Fire is a traditional way to prevent excessive bleeding and is a standard loophole for this sort of problem. For example, how to kill a hydra:

To defeat the Hydra, Hercules called on his nephew Iolaus for help. As soon as Hercules cut off one head, Iolaus would cauterise the wound with a flaming torch so that nothing could grow to replace it. - Wikipedia


Remove the arm entirely to go back to two arms.

When an arm is cut off a joint grows from the wound. From this joint grow two new arms. Cut one of these arms and you get a total of three arms.

Here's the important thing: The joint itself still counts as one arm. So if you cut through the the joint you end up with two arms and not three.

That means you can always reset to two arms by cutting the arm off entirely at the shoulder.


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