Sister hissing at her brother

Question
I have two Siamese cats - a brother and sister.  The brother recently spent a week at the vet with a blocked urethra and distended bladder that didn't let him pee on his own.  He's back home now (and everything is going great!), but ever since he's been home, his sister hisses at him whenever he gets near her.  She's only hissing at him (not the dog or any of the people in the house).  Any thoughts as to why she's doing it, or what we should do?

Answer
Karen,

That is a perfectly normal behavior. Cats go by smell and not by sight in recognizing other cats (with humans, they go by voice...not by sight). Your cat brought home MANY different smells from the vet: office smells, medicinal smells, and smells of other cats...all clinging to his fur. The female cat thinks he's another cat! She is protecting her territory from this 'intruder'.

You can, if you want, keep the cat who just came from the vet separated until he absorbs the normal smells of home again. When he grooms himself he will be replacing his regular scent. You can also rub the cat who did not go to the vet with a towel, then rub the cat who did go to the vet with the same towel to transfer familiar smells but do not do it the opposite way because you will then be transferring the vet's office smells to the other cat!

A trick that I've heard a lot of people use in that situation (though I have never tried it) is to put a tiny drop of vanilla on each cats forehead so they smell the same.

Things will settle down when the smells are gone from him.

Tabbi