Cat sibling jealousy

Question
Yesterday my grown son took one of our two (indoor only) cats to the vet,
the other stayed home. These are 8 year old female litter mates, usually very
loving and protective of each other. I came home from work last evening,
and the cat left at home was hissing at the other one, won't let her near,
won't mutually groom, etc. It is still going on this morning. Is this normal?
Is it a kind of sibling jealousy because one went out? I have only had them
in my home since November, they lived with my son most of their lives
prior. Any insight would be greatly appreciated. Thanks!

Answer
Hi
i would say that this is not jelousy as i don't think it is an emotion cats have. they are more driven by territory, food and scents.
It sounds to be like something called truam aggression. this is a strange phenominom where one cat is frightened by something, it could be anything and for some reason blames the fear on the other cat and so reacts towards the other cat in a fearful agressive way. the problem is the initial fear could have been anything, froma loud bang, to having their tail stepped on.

The only thing that will cure this is time and also reinroducing the cats to each other again slowly over a week or so, i know this might sound a little drastic but if it is not handled correctly the fear coould increase to a level that cannot be altered and they may always be aggressive towards each other. the best advice i can give you is to go through the intoducing cats to each other described here on my webpage /introducing-cats.html
and hope that it doesn't take too long before your cats settle down again.
best wishes
kate