Porky
Citizen of Zooville
I'll admit I'm beyond stretched out (constant constipation problems since early childhood, my superpower is clogging toilets), but:I just don't think my ass could take a knot though, tbh.
(1) knots aren't rock-hard, they are somewhat soft and pliant, and
(2) dogs expand more after penetration, so what goes in through your O-ring is much smaller than what inflates and ties you, and
(3) all you have to do is take a look in the toilet to see how big of a diameter can get pushed through, then pick a knot no larger than that.
The big problem is when they get distracted and try to wander off (or "oh look a squirrel" *vroom* off oh look rectal prolapse, rectum? kil't 'im) before they start deflating again. Kind of surprised people don't tie a leash to the bedframe or something.
That said, I've seen a couple of anal knotting videos where the woman obviously got torn. One was a small, skinny woman, probably Russian, on a yoga mat with a dog whose knot (when he pulls out) was HUGE, and when the dog pulls out you can see that the big gush of cum pouring out of her ass is blood-red. For that matter, I injured one of my girlfriends once because she couldn't relax enough and she ended up with a few small tears in her O-ring. May have been from not using lubricant since it was both our first times ever trying that and we were young and dumb.