When Sara Sidle checks Rascal the cat's wound, the wound does not move in same way as Rascal's fur, but floats over it, showing that the wound is an optical/visual special effect.
Grissom comments that since cats were domesticated "only" 4000 years ago, they still retain many wild instincts. This line appears to be a misreading on the writers' part. At the time the episode aired, the oldest known evidence of domestic cats were Egyptian paintings from around 4000 BC, thus meaning that there had been domestic cats for at least 6000 years (new archaeological evidence published after the episode aired revealed that there were domestic cats in Cyprus and the Levant before that date, possibly going back as far as 9500 years ago).