Background: We adopted a rescue cat just over a week ago. She’s a really loving cat, 1 year old, and loves a fuss. She was found in a garden after birthing a litter of kittens and spend so much time feeding them that she got sick. The kittens were rehomed, she got better and we adopted her from the RSPCA. 

My resident cat is a 12 year old male, really chilled out, good with other cats and mostly sleeps all day. 

We’ve kept our new cat in her own room for the most part and occasionally let her roam around upstairs while our resident cat is shut downstairs. We’ve been doing scent swapping and trying to feed them on opposite sides of the door but she doesn’t always eat straight away so that hasn’t really worked out. I’ve been giving them both treats instead but again our new cat won’t always eat them, especially if she knows our other cat is there. 

Our resident cat snuck into her room as we opened the door a few days ago and when our new cat spotted him she hissed so we quickly took him out. Resident cat has been really curious and waiting outside the door smelling under the gap, but our new cat hisses at the door if she knows he’s there. He has also started hissing at the door in retaliation which is unlike him. 

It’s only been a week so I know these things take time but the fact that they’re hissing when they can’t even see each other has me doubting how this whole slow introduction is going. 

Cat introduction going badly