I have 4 rescue cats. I didn't want any of them but I couldn't say no to any of them either and they're all my babies now.
They normally all live together in harmony and have for years, although tabby cat and fat cat give an indignant hiss if feral kitten or ragdoll cat get too close while playing.
Anyway, today I was lay in bed with tabby cat having a cuddle, when feral kitten walked over. Tabby cat gave a hiss and feral kitten walked away into the hall, looking through the bannister railings.
No word of a lie, tabby cat sneaked off the bed, and crept up to feral kitten on 3 legs, with one paw sticking out at the side, got behind feral kitten then pushed her through the bannister railings and down the stairs! 
Then, later in the day, fat cat was just about to walk down the stairs and tabby cat did the same to her! Although she didn't manage to push her anywhere because fat cat is very very fat. But still.
I've never seen such underhand behaviour!