Rhuby notes: In any case, unless it is a moving picture, you do not have any idea whether the train is travelling forwards or backwards, which is a significant factor in solving this particular urgent problem.

In this particular case there was a railroad worker who was about to leap onto the train and we could tell from his stance which way he was going to jump. The particular urgent problem was that the train was a runaway with hazardous chemicals on board. If it derailed and dumped its contents in a highly populated area it would have wreaked untold havoc.