Is my boy trying to mate his sister???

[Alsoflamingo]

We have a pair of 3 year old cats - both 'done' ages ago. But the boy often appears to 'mount' his poor small sister, holding on to scruff of her neck with his teeth to hold her in place. Is he trying to mate her poor bastard not realising his equipment doesn't work - or is it something else? She doesn't seem hugely bothered. Just wondering….

Sounds like it. (Mating between cats can be pretty violent at times.)

Is he showing any other signs? (I'm wondering if the vet did their job properly.)

Definitely seems like mating behaviour!

I have 2 neutered male cats who do this to cushions and our clothes. Thankfully not to each other.

They purr very loudly when doing it, and sort of pedal their back legs - not to be confused with the rabbit kick disembowelling rabbit kick they employ when play-fighting.

From what I've read, I believe it to be associated with asserting dominance.

*Over-use of rabbit kick there!

Yes if they're brother and sister they'll do it... my poor siblings (brother and sister now dearly departed) the male got very amorous and his sister hated him anyway but didn't help if he was trying to mate her...

Didn't also help they had a huge brother living next door (the neighbours took their brother to live with them) who probably tried it on but strange to say he had a lot of respect for his sister...

I had rather assumed that if they had both been neutered the urge would have gone, but it appears not!

OP - oh no.... despite having their bits being taken off them it seems they still have hormones and urges...