Number one graps the pole and zap. Number two grabs the pole and zap. What was Number three thinking? The first two just happened to fall down there in the water next to the pole and go limp for no reason? Even if he didn't actually see the others grab the pole, a little thought there should make him suspect some connection.
It looked like he lost his footing, tripped or slipped, and instinctively reached his hand out to catch his fall.
edit: Watched it again, I guess that applies more to the second kid.