Two of my cats have "love/hate" relationship. One minute they're grooming each other and the next he's hissing at her (if she rushes up to him to play). She hasn't learned he doesn't like surprises and he hasn't figured out she's not out to hurt him. I wish I could sit them down and have a little "chat" on how to play nice and get along, but I suppose spending 24/7 together can cause some issues.