i have a male 5 year old cat that i have had since he was a few months old that is neutered & i just brought a new female kitten home about a week ago. i introduced them & everything & the older kitty just sniffed her & walked away so i thought he didnt really care about her being in the house. well today i caught my older cat sitting at the door to the room where my new kitten is & the older cat was hissing so i was wondering if it would not be such a good idea to let them be around each other?