Otherwise, why we don't stink all the time?
I really can't speak about the human end of this question...
But, I can assure you that many of my 'mechanic type' friends swear (literally), that the sphincter in the frog anus is water tight.
I have assumed this to be correct on many occasions, myself.
Wow, what an awesome question.
I can see by looking at my past posts that were removed from the forums I might need to produce more suitable topics for discussion like this one.
Are you sure you don't?
Also, most of what's released in Nitrogen, which is odorless.
They also obviously "blow off excess pressure" from time to time....so while "air tight", this does seem to have a "air tight up to a certain pressure" qualification.
Some also seem to have discrete leaks that were (Claimed) to be undetected by the owner of the anus, albeit detected by proximal organoleptic receptors, which are swift to alert said leaking anus owner of these otherwise discrete leakage events.
There are actually two anal sphincters, plus some valve-like folds in the anal canal between them. The valve-like folds ensure that when you pass flatus (that's the technical term for gas or fart) it's only flatus that escapes. Is the external sphincter airtight? That's the one under voluntary control, so probably the one you're asking about. I don't know for certain, but I doubt it. More likely, the small, continuous "leak" is just too insignificant to notice. Think of a beachball with a tiny pin hole in it. You can still fill it with air, and it'll hold most of it for a while, even though a little bit is always escaping. The more deflated the ball, the less pressure is pushing toward that hole, so the leak slows. Though, I'm not sure if there is a definitive answer. Then again, there are some obscure anatomical journals that publish a lot of weird things you never knew anyone wanted to know.
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