Twelve marbles roll into a tree of brass chutes, and at every fork a toggle sends one marble left, gets tipped over by it, and sends the next one right. So every fork halves the stream. Cup three sits under the shortest, straightest way down. But the pipe that seems to lead to cup two is capped: it holds two marbles and then spills through a notch into the long zigzag, so cup one at the end of the slow way gets a double share and fills first, every round. The red marble lands somewhere different every time, and the waiter rings his bell whenever a cup is full. But one part of this machine is worn, and it is not saying which.

Every knock and every music-box note is timed by the machine itself.

Stay for the end.

Which cup did you pick?