A thief can unleash a vicious attempt at slicing through a target's hamstring.
If successful, the victim's legs will be weakened, and they will be unable to
mount.
If a thief attempts to attack the hamstring of a mounted victim, both the
mount and the victim will be harmed, but the thief will be unable to successfully
slice the victim's hamstring.
Due to their spectacular horsemanship, Cobar are able to mount even after
having their hamstring cut by a thief.