Tonight on PRI's The World there was a story about the wildcats in Scotland. Here's a link to the story reported by Ari Daniel Shapiro.

Here's a good look at one, and I was going to look this up when I got home today anyway, even without your thread. They described them has having a tail that on a domestic cat would get puffed out when they're angry. On the wild cat the tail is always looking puffy.

SRS