Priests were metal-reinforced overshoes. They saved your soles. This is an Assassin joke.
Terry PratchettA lot hinges on the fact that, in most circumstances, people are not allowed to hit you with a mallet. They put up all kinds of visible and invisible signs that say, 'Do not do this' in the hope that it'll work, but if it doesn't, then they shrug, because there is, really, no real mallet at all.
Terry Pratchett