a friend of my killed a rat by scaring it into having a heart attack. it was pretty funny. the mouse was running around one moment, and the when it was surrounded by 4 huge guys, it just dropped dead.
If your cat brings in a shrew, or a mouse or a vole that's still alive, you've got to be careful that you don't scare it, else it'll crawl into a hole, have a heartattack, die, and stink out the house until you can find it.