One of the most iconic sequences in the Tunnel course involves a chain reaction of Electrode. As you enter the main cavern, you'll see several Electrode scattered around. Your goal is to make them explode in sequence.
Start by throwing a Pester Ball at the Electrode closest to the track on your left. This will cause it to explode. Then, quickly aim and throw Pester Balls at the subsequent Electrode as they appear or are revealed by the explosions. Successfully triggering all of them will clear a path and reveal a new area with a Zapdos.