The mind of a wizard is more open to the more esoteric elements of his surroundings Ã¢â?¬â?? this is why he is able to perceive the weave of the Great Tapestry that is the multiverse, and pull at the strings. This increased sensitivity can manifest in several ways.
A master thief is struck by an insanity spell and thinks he is half cat. He walks around sniffing things, clawing the furniture and licking himself in the manner of a grooming cat. This is a major cause of embarassment to the guild and the master thief must be cured of his insanity.