I have got two foster cats in at the moment, they didnt know each other before i took them on. For the first couple of days they were in separate rooms as one was freshly neutered, so i didnt want them fighting. After a couple of days i took her into the room with the other cat and just sat with them for a while. There was growling and hissing but nothing more. They now get on really well, but the eldest of the two (she is 2 and we think she has been an only cat all her life) will go up to the other cats to sniff them, and when they get close to her, will move her head back, put her ears flat and growl or hiss at them. She does seem to have stopped doing this with the other foster, but if she goes for a nose sniff, she will back off first. Any reasons why this might happen?