My cat lashes his tail and purrs at the same time. Does that mean he's happy or mad?

He's probably happy, cats don't really purr unless they are... do they? Lol

About.com: http://www.messybeast.com/cat_talk2.htm shows cats body posture etc... you will find it very interesting.

Actually, a cat will purr when in it's irritated and/or in pain as well. For instance, a cat giving birth will purr through the contractions. Domestic animals still carry the habits of their wild ancestors and one of these is to not let other creatures know they are hurt, sick or in pain. It's all about survival. Many cats can appear healthy when they are quite ill, which results in them not getting veterinary treatment until they can't hide it any more. One of the things they do to appear healthy or strong is purr.

So, you have to look at the overall, long term behavior of you cat to determine whether he is happy or not, as well as other physical clues, including eating, drinking, and litter habits. Hope this gives you some guidance as to your cat's situation.

Didi

The lashing tail is a warning.

Yes, a cat can purr when it's angry, frustrated, contented, in pain. Body language and "tail language" are the best signs as to what a cat is thinking or feeling.

I think my cats purr when they want me to do something, like feed them, or let them out. They seem to think it's a good way to get my attention. They also purr when I pick them up when they don't want to be picked up. I think they are using it the way people smile sometimes to indicated submissiveness more than happiness. Just an educated guess.

It depends I used to live in a household of five cats and noticed that when my cats switched their tail and purred it usually followed by a roll on the back and a playful bite and kick.