In Heinlein's Stranger in a Strange Land, Jubal thinks he sees Mike cut off one of his fingers while cutting up an apple.
He handed the glass to Anne, then took the fruit knife and sliced off a chunk of apple. It seemed to Jubal that Mike sliced off one of his fingers... but his attention was distracted as Duke passed the glass to him. Mike's hand was not bleeding and Jubal had grown somewhat accustomed to legerdemain.
So Jubal dismissed this as some sort of trick. But what is the point of it? I don't see it referenced anywhere else in the story.