Cat Puffing/Wheezing At Other Cat?

[dustytiger]

So I've been trying to introduce my two cats to each other and one of them growls, hisses and puffs(??) at the other cat? I separate them before they can fight and I'm trying to take it slow and get them accustomed to each other's scents, but I've never seen a cat puff like that.

It looks like she's literally blowing air out of her mouth after inhaling it from her nose--She even seems to be trying to purse her lips as much as a cat can. Is this normal for some cats or should I be worried?

 

[missriss]

My cat gets puffy when he is trying to be tough too. He doubles in size! It is very funny to watch, but normal defense behavior. Cats can make all kinds of weird noises so I wouldn't be concerned about the puffy/noise thing. Just a sign he does not like the situation he is in. Introductions should be really slow with lots of food/rewards.