My cat hisses and swats at its tail, doesn't eat wet food, and scavenges people food. Why?

We got this cat as a newborn, found in our backyard. She seemed to be abandoned, and now she's 8 years old with a couple of weird problems. She hisses at her tail, and honestly appears to get angry at it. She hisses, growls, and swats at it. If you try to pick her up or put her away while she's doing that she usually screams, like really screams, and bites/scratches. She doesn't go after her tail as much any more, but sometimes she spontaneously just starts hissing and growling like she's annoyed, and works herself up into a rage. After she gets to the point where she's angry she'll usually run away to a favorite sitting spot, and then the cycle will continue.
Also, she barely ever eats wet food. She eats a lot of dry food, sometimes so fast that she throws up, but isn't interested in almost any of the wet food we try to give her. She ends up eating people food that will sometimes make her sick, like hotdogs, chicken, butter, etc. Any suggestions with either of these problems? thanks.

Asked by Member 1083743 on Jan 11th 2012 Tagged hissing, tail, growl, growling, hiss, anxious, anxiety, angry, mad, people, food, not, eating, starve, scavenge, vomiting in Aggression