Thanks, Becca. That's good to know. Keep in mind that for a cat a traumatic event might be one the owner doesn't even know about - a sudden clap of thunder, an auto wreck in the street (with sirens and excited cries) or a big dog coming onto their property.

Maybe Phil should try giving his two cats special treats together, so they associate one another with nice things.

About male vs female - My friends with lots of cats say that among cats, females are dominant. We once had a male cat and added a female. They never did make peace.