It wasn't that Nanny Ogg sang badly. It was just that she could hit notes which, when amplified by a tin bath half full of water, ceased to be sound and became some sort of invasive presence.
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