A square sheet of paper is folded in half from left to right, and the folded sheet is then folded in half again from top to bottom. A small corner is snipped off the one corner of the folded packet at which both fold lines meet. The paper is opened out flat again. What does it look like?

The corner where the two fold lines meet is the point that was at the very centre of the original sheet. Cutting there removes a small piece from all four layers, and when the sheet is opened out the four cut pieces sit round that one point and join into a single hole in the middle. The trap is four corner holes — that is what you would get by snipping the opposite corner, the one made of two open (uncut) edges rather than of two folds.