Since this is a form of Augmented Tail (and technically what inspired me to create this group), I decided to include this as a sticky thread that will hopefully help with their writing.

After doing some research, I found what might have been the original creator of the Tailmouth and what their definition is for it, so here it is:

reposting from my FA journal, I wrote this a while ago.

I've had a few people ask about my interpretations of tailmouths, and now I've really had time to formulate how they live and work I thought it'd be cool to write up an info post!

This is just my interpretation of them - yours DO NOT have to be like this (actually I might prefer it if they weren't). You can change anything and everything, it can be completely and totally different, I don't want anyone to feel like this is the "official" way the species works or whatever.

For a tad bit of info first, in my worldbuilding there are humans, "demihumans", normal animals, and "demons". Even within the world the distinction between demihuman and demon is somewhat blurred though most people consider demons to be demihumans with magic basically. Demihumans and demons are human-like creatures, sometimes fur-covered and sometimes with human skin, that usually have some sort of animal distinction - ears or tail or whatever. Tailmouths are a type of demihuman.

Also, "tailmouth" is the word for the body, "mouthtail" is the word for the tail. lol.

- PHYSICAL -

Tailmouths and mouthtails have completely separate personalities, tastes, and urges, which often leads to some conflict between the two. The mouthtail is an extention of the spine as a normal tail would be but has its own complete digestive system that merges with the body's at the large intestine/rectum area. Both bodies benefit from the energy created by digestion no matter which system digests it, and both share a nervous system, so they feel pain at the same time and can tell what the other is doing even if they are not otherwise paying attention. That said neither can completely control the other, though they can influence movement, especially if the other is not fighting it. For example, if the tailmouth is walking in one direction and the tail wanted to suddenly turn, it could make the body move the direction it wanted to, if only for a few moments since the body's natural reaction would be to fight that urge.

Though the mouthtail does not have its own brain it 'thinks' for itself, and the body and tail cannot tell the other's thoughts, though how this happens is unknown - most attribute it to either some sort of inherent magic within the tail or that the tail occupies its own separate section of the body's brain.

The tail itself has its own flexible 'ribs' that extend out from the spine that are made of cartilage, not bone, so while they give the tail some basic support and protection they are not particularly strong. They make up for this with extremely strong muscles, particularly around the jaw, and a formidable set of teeth - not much will really want to get close enough to injure it. The tail also has a small set of 'lungs' (not anything like the lungs of a mammal, more like a set of bellows) solely to circulate air through its great maw so that it can talk and make sounds. A mouthtail can live just fine without these lungs - some develop without them - they just will not be able to speak.

In rare cases, a tailmouth will have a small, puffy tail like my character Kuwan and her tail Yauma. This is usually due to extreme illness or malnourishment as a child or some sort of other issue while the tail was growing, leaving them with a malformed digestive system in the tail that can not work. The drain of energy of maintaining a tail while not receiving the benefits of their systems usually results in a weak tailmouth who will most likely die without the care of others. For KuwanYauma, though she is often ill or weak, she lives by seducing others and attacking them and killing with her mouthtail's strong jaws while they are distracted as she would definitely lose in a 1-to-1 fight.

...Basically, the best way to think of the tail is as a parasite that has a symbiotic relationship with the body.

- SOCIAL -

Since in my stories there hasn't been a technological/industrial revolution yet, tailmouths aren't modern, but more tribal. Some live in (usually) very small groups/family sets of maybe 10 - 20 individuals, some are completely solitary, and a few live within groups of other creatures or humans. In general they aren't very trustworthy because they need to eat a significant amount more than other human-esque creatures and their culture, while not supporting cannibalism, doesn't discourage it, either, so many are quite violent towards demihumans or humans, and some are violent towards other tailmouths, too.

A tailmouth comes to be when

A) a tailmouth parent has a child - they can both be tailmouths or just one. If the mother is a tailmouth, the child will always be a tailmouth. If the father is the tailmouth the child will be a tailmouth maybe 75 to 80% of the time.

B) a tailmouth is killed by someone. Through some unknown force the tail is transferred to the killer. A small growth will form at the base of their spine that will grow to become a mouthtail within a year. Though extremely painful, it can be removed, however (though this is essentially severing their own spine at the base, so people that do this will have a multitude of health problems including digestive issues, and often the psyche of the mouthtail will not leave even after the tail itself is cut off, leaving the body with a 'voice in their head'), so most people who begin to grow a tail will remove it before it becomes a mouthtail. This is also how tailmouths have more than one tail - if a tailmouth kills another tailmouth, a new tail will grow above their own. It's not known how many mouthtails a tailmouth can have.

Related to B), essentially what is happening is the mouthtail is imprinting itself on another body before it dies, so if no-one is around during the death process they will perish completely. In some cases, innocent bystanders can be imprinted on and will grow the tail, but usually the mouthtail imprints itself so it can torture/exact revenge on the killer and will not bother imprinting itself on any random person, since it will most likely be cut off, which will force it to live as a bodiless entity attached to a hostile body - torturous for both participants.

Some tailmouths and their tails live in perfect harmony together, some end up killing each other.

Ummm I think I touched on everything I wanted to...
Any questions? Anything else I should talk about? Hahah

Also, do any of you guys have your own interpretations of tailmouths? What are they like?

I hope this has been very helpful and insightful for all of you.

Can I expect multiple stories about a tailmouth pony?

With a talking mouthtail.

7113259 I am thinking of maybe writing a story with a Tailmouth in it. Though there are a few other projects that I would like to finish first.

I've had a idea for a while bouncing around in the back of my head.

It would focus on a Mawile type pony ...

Though this tail would be the sole controller of the body, the pony body actually just a front kind of like a puppet. The tail able to talk, and also throw its voice to create the illusion of the pony talking. I've teased the idea that this pony is found by a hunter stallion and thinks he's chasing a common thief pony, but when he catches her, becomes smitten and ends up falling in love with the puppet. Unknown that it's actually a monster. But that's just a tiny shot in the dark at the idea.

This is very interesting indeed,

If maybe anyone has a better idea or tips... I'd love to hear them.

I could see myself maybe writing it out more seriously now.