Begin this trick by explaining that the goal is to get all three cups facing up after making exactly three moves. In each move two of the three cups must be flipped simultaneously. After this explanation, place the cups on a table in a row so that the center cup is facing up, and the two outside cups are facing down. This initial setup is critical for successfully performing the trick, and understanding how it works, but you should not draw attention to it. In fact, as soon as you set them up you need to start flipping the cups as practiced. The trick works because the audience concentrates so hard on your moves, that they don’t remember the initial setup. At the end of the three moves when you have all the cups facing up the solution quickly flip the middle cup over so that it faces down.
Next, invite one of the students who was watching to get all the cups facing up in three moves. This is impossible, because the cups are now in a different starting position, but it is a rare student who realizes this. In fact, the student usually begins to flip the same cups you did (students were watching the moves not the initial conditions). The student will either get all the cups facing down or stop in puzzlement before the third move as the realization strikes that there is no way to get all cups facing up in one more move. If the three cups are all facing down, I tell the student that the trick has not been done correctly since the cups were supposed to be facing up. I then flip over the middle cup so that it now faces up the original setup and quickly do the three moves once more to prove that it can be done. After getting all the cups facing up, I flip over the middle cup, once more creating the impossible starting condition, and ask for someone else to try the trick. If the cups are not all facing down at the end of the student’s moves, I quickly set them up correctly and do the trick again to show that it can be done and then mischievously flip over the middle cup creating the impossible starting position once more. I continue to perform the trick until some students catch on that it is the initial starting position that allows the cups to all be facing up, not the series of moves.