Cats can have serious mental issues. I did animal research in grad school, and we sometimes used cats. We recieved animals due to be destroyed from the animal shelter and the experiments, while terminal, were done in a *very* humane manner.
We had a standing policy that anyone in the lab, for any reason, could claim the test animal prior to the experiments and the lab would eat the $450 fee that the university paid. I've always been good with cats and one day I went to pick-up an animal. The cat was charming... purred and marked my hand... was a real charmer. I spent about 3-5 minutes with it and thought "why on Earth would someone not want this animal?". Well, I was about 85% convinced this would be the animal I claimed and saved. Then, suddenly with zero warning, it opened my hand up between the fourth and third knuckle half-way down to the wrist. Needless to say, bootsie wasn't claimed.
Some cats are just nuts.