I have two cats that basically up until now have refused to acknowledge that the other existed.

Our original cat Schatze is umm...a bit of a loner. He's not a regular cat-type cat, he's aloof and perterbed most of the time. (Well now that I say that it does sound like a regular cat-type cat - but..it's different). He doesn't appreciate any attention, he doesn't purr, and I'm pretty sure he'd be happiest if we all moved away and left him here in the neighborhood on his own.

Then we got Marla who is a bit more personable and playful. She is a very communicative cat, and will actually come and meow at you and lead you to something she wants. (Like the front door, or her empty food bowl)

Marla had established herself as Alpha as soon as she got here. We worried at first if Schatze would be mean to a new kittie, but Marla took over immediately and seemingly laid down the law for Schatze. Up till now they've basically ignored each other.

But now all of the sudden they are interacting all the time, and I'm not sure if they are playing or fighting. One or the other will give chase, and then when they corner the other they both start swiping at each other. Sometimes balancing themselves on their back legs and boxing like kangaroos. Sometimes there is hissing involved, mostly not. They do this for long periods of time, nearly every day now. Chase chase chase, box box box. More chase. More box.

So I'm asking the cat people out here - are they fighting or playing? And why now?