Norm and Ray were about to sit down to a game of chess when Sally walked in.
"Still playing the same boring game?" she asked, "Let me make it more interesting. I'll set up the pieces on the board a little differently."
"OK," they said, glad to let someone else take care of the chore of setting up the pieces. When they sat down to play, it seemed that only a few pieces were in an unusual position.
"Come on, make your move," said Norm. But when Ray picked up a piece to move, Sally said, "No, that would be illegal."
Ray's brows furrowed for a minute, and then he saw that she was right. He pondered the board for a few more minutes.
"I can't move," he said, "and what's more, neither can you."
How had Sally set up the board?