First, the waiter stuck the match into the lemon wedge, so that it would stand up straight. Then he lit the match and put it in the middle of the plate with the lemon. He placed the glass upside-down over the match. As the flame (火焰) used up the oxygen in the glass, it created a small vacuum (真空), which sucked in the water through the space between the glass and the plate. Thus, the waiter got the water into the glass without touching or moving the plate.