How could a human and a centaur do the do without the human suffering serious injuries?

Question

The best weapon for centaurs is a human on their back.

Now, the nature of this companionship tends to form really strong bonds between centaur and their rider, since they literally have to protect each other's backs.

Thing is, when I take a creature from a mythology, I also tend to lift "background" elements from it, for flavor, which means that bisexuality is the norm here.

So, centaur and rider are bound to get more close and lovey dovey in the downtime. While the human "riding" the centaur should be safe, the reverse is most definitely not, just look at the story of Mr.Hands (NSFW).

The army wants to avoid such embarrassing and unnecessary casualties and since people will be people, they know they can't really stop them, plus it does seem to have positive effects on the morale (and don't ask why is there a Wikipedia article about this)

The best way to deal with this problem is to make sure that at least if they do it, they do it safe (finding contraceptives isn't an issue, internal bleeding is). But how can a reverse ride be made safe for a human?

Since the budget, as well the number of desperate engineers with no sense of shame are limited and because it's a private thing, it'd be preferable if this safe way didn't require any tools or extra people.

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Centaurs

Centaurs here are slightly different from myth. Namely, they're more similar in attitude to Cyllarus, Hylonome (because Ovid is also a fan of monster girls) and Chiron.

As far as anatomy goes, they are... strange. Two hearts is nothing new. The human and horse spines are joined with an L junction that's made up of many small vertebra that get progressively fewer an larger with distance from the L junction. The rib cage is kind of wacky as well, since it has to bear the load that is the human torso. I can't really describe it, but it's obviously very different than what a horse has.

The human part has a stripped down digestive system, while the horse part is modified to be able to digest meat and now has a much stronger gastric acid and more enzymes to nuke the million and one digestive diseases that a horse can get.

The horse part has a height of 155-165 cm at the withers.

Centaurs breathe through their mouths during intense exercise and are generally lower-speed endurance runners with decent sprint-bursts. They also like to cosplay as Polish winged hussars.

Answer 1

Heh heh. Somebody has been watching Epic Movie.

https://www.imdb.com/title/tt0799949/?ref_=fn_al_tt_1

John Varley's Titan series include's many helpful suggestions.

In particular, centaurs are dual equipped. They have a very-much-more human scaled set at the front between their front legs. And a horse-scaled set at the back in an arrangement similar to horses. The centaur reproductive sequence is a bit more complicated, as one might expect from a chimera-like species.

Indeed, they are more than dual equipped. At the front a centaur has either male or female equipment, determining the sex of the individual. At the back they are equipped both with a penis and a vagina and uterus. Thus they can perform functions corresponding to their front sex with front equipment. And they can function as either male or female, with appropriately sized individuals, with the back sets.

Answer 2

You’re the one envisaging the design of these centaurs. Just make sure everything is appropriately scaled.

If you’re dead set on 1:1 horse scale:

The human body is remarkably elastic. Just look at what can be achieved by gymnasts, contortionists or even people who do yoga. Muscles that usually stay taut can be relaxed and stretch to a remarkable degree without suffering damage and then return to normal. Not only that but the appropriate.. parts are among those more designed to stretch and return.

With sufficient time, training and care (especially on the part of the centaur, who could cause serious damage if they got too vigorous) the human body could probably accommodate the majority of centaur.. measurements.

With a little joinery (and upholstery for comfort) building a frame capable of taking the weight of a horse while permitting a human inside (and parts of a horse too) is almost trivial. (Looking at you, Sacred White Bull of Minos), though you can likely get away without this if the centaur is alright with a tupenny upright (a curiously quaint phrase for doing the deed standing up) and the human has no regard for the health of their knees and back.

This would not be a casual affair for either partner. It would need months, maybe years of training and preparation to avoid sprains and tears on the part of the human, a frankly astonishing level of restraint on the part of the centaur, a level of trust and communication between the two that would make them the closest of lovers, and an awful lot of lubrication.

So. By the time this... act... can be done safely your couple will already be so intimate that they’ve probably already figured out alternative arrangements. Get your centaur/human sergeants to surreptitiously pass around pamphlets detailing the requisite training cough exercises, safety precautions (go slow, pay attention, don’t get excited, use an awful lot of lubrication), and alternative intimate practices.

Now if you’ll excuse me. I need to find the nearest bottle of brain bleach.