It's dominance behavior, might be misdirected/redirected aggression given that laser pointers are sometimes overexciting or frustrating for cats. Cats (any animal really) can get weird with lasers, since they can't catch the target, and if you have an irritated/frustrated cat then resource guarding behavior gets weird, with an object that essentially doesnt exist, and nobody can actually have or guard. I'd quit the laser pointer, and try other toys for play. If Phillip is still mounting i'd consider talking to a vet with behavior experience or a behaviorist, to try to nip this in the bud. Its essentially bullying between cats and can distress the recipient a lot over time.

Ive never seen mounting result in that kind of injury, but i guess its possible. Cat penises are small, but have spines, which are infamously painful. I'd keep an eye on it, if you see any other indication of injury, inflammation/bleeding/poop problems head to your vet. This kind of thing can be from lots of issues, could just be an oddity as well.

So lil man on the left is Terrance. Slightly bigger man on the right is Phillip. They’re littermates, turned 2 in October.

Occasionally Phillip will attempt to mount Terrance. Terrance can be a rascal but at the end of the day he is smaller (we’re pretty sure he was the runt). The mounting attempts almost always happen when Terrance is excited by the laser pointer. Phillip senses his energy and I guess thinks it’s…time to get sexy or something? Or time to knock Terrance down a peg by dominating him or something? He sort of jumps on him and forces him into a crouch position, bites the back of Terrance’s neck, like males do to immobilize females for mating, and then tries to get “into position”, at which point I usually scream out of horror.

Now I’ve always figured that actual penetration between two male cats would be difficult if not impossible.

But just a few minutes ago I noticed something that concerned me. Terrance had a slight rectal prolapse. It was small but EXTREMELY noticeable, since he (sorry if this sounds weird) keeps a very tidy anus. It’s always clean, minimal crust, and not like one of those big ol’ cat anuses that looks like it’s staring into your soul. He was playing in the sink at the time, batting the strainer around, half in and half out with his bum up in the air.

Fortunately he sort of sucked it back in right away and you never would know that anything had been out of place but it freaked me the hell out. My boys are on a wet food only diet for dental reasons, and they have healthy poops, so it’s not as if he strains to poop or anything.

So I guess what I’m asking is…can a male cat physically rape his brother? Should I take him to the vet about the prolapse, even though it went away immediately and went totally back to normal?

Thanks, ladies!

I don't have any advice other than what's been posted, but your boys are very cute

Mounting behavior post neutering is just dominance and not particularly sexual in nature. Neutered cats, especially those neutered at such a young age would not have developed normal sexual urges. Most neutered male cats do not mount but younger cats sometimes do.

While it is not all that strange for Phillip to play-mount, it is strange if he is able to maintain an erection post-neutering. His hormone levels should be checked to make sure his testosterone levels are normal for a neutered male.

So, considering what is physically normal it is unlikely that he penetrated Terrance and what you glimpsed is likely just normal weird butt-hole stuff - but of course get him checked out if you think otherwise.

However, the interaction of these males in the whole mounting behavior scenario is unpleasant to watch and unpleasant to be Terrance.

Would you consider getting a third cat? This would definitely change the dynamic between the two brothers. I would highly recommend a large-framed female because in cat society, the females are usually the bosses. Ideally, the larger framed female does not have to be bigger than Phillip, but should be at least as large as Terrance.

She would not put up with the boys acting up with her or with each other. If Phillip tried to mount her she would read him the riot act. Her presence in the house would modulate things quite a bit.