Corrected entry: When Ace is going to inspect the tank, he climbs halfway down the ladder and jumps down. Then he takes a few steps and makes it nearly halfway across the tank. In the next shot, they zoom in on Roger and Melissa, but you hear about 7-10 more steps, enough for Ace to reach where he was going, but when they show him again, it looks as if he's barely moved, if moved at all.
Jazetopher
18th Oct 2006
Correction: You only hear the steps, but since we can not see him, there is no indication that they were all in the same direction. He likely took the same number of steps backward as he did forward (i.e. five forward then five back) to end up where he started, or even walked in a circle investigating the perimeter of the tank.
Jazetopher