Here's the scenario. Muffin and Zoey are on the cat tree, Muffin on the lower level, Zoey on the middle. Muffin is doing this thing she does where she grabs the post and kicks it and bites it. Zoey leans over the edge of her platform, watches for a minute, then reaches down and slaps/bats Muffin. Muffin jumps up, slaps back, chases her up a level, and they slap eachother a couple more times. Then they lay down and look out the window again. No hissing, no sounds at all, no puffed tails. They did have flicking tails and "wild eyes". Zoey and Tiger chase eachother some and I'm sure they are playing, but I wasn't sure with the addition of the slapping/batting. I have never had cats that interact with eachother much at all, so cat to cat body language is new to me. I literally sat and watched this today instead of tv.