There's one of the paradoxes with SR that I've never actually seen an answer for. There is a man on a train traveling at a velocity where length contraction starts to matter. Say, .3c. There are some dirty bandits that have rigged up a trap door system in a mountain up ahead on the tracks. There are two(currently open) doors on either end of the mountain, which is the same length as the train. The dirty bandits know how fast the train is going, and they have made it so that at the appropriate time, both doors will shut while the train is inside. The train will see the mountain as length contracted, and the bandits will see the train as length contracted. Does the train get stuck in the mountain or does the exit door crush it?