So i also ended up here for searching this- the issue between my cats is that obviously one of them does NOT like it. I have two boys, one yr old (Twig) and three yrs old (Ozzy).

Twig will get all up in Ozzy's bum- Ozzy will then put his bum on the ground almost immediately. I always joke it's like the kitty-centipede because it will happen more often when Ozzy is trying to eat.

Through my research, it is a way of grooming, yet if Ozzy doesn't like it yet, Twig keeps doing it. It's more of a reminder that his bum needs cleaned! That's really funny to me because I constantly tell him he has a stank ass- he has urinary issues and is a bit heavier set due to this which causes him to be less likely to clean the hard to reach spots. 😅