Dr. Gordon Freeman stacked three boxes up and jumped the fence into the trainyard to look at the train that would take him away with Alyx from the Citadel about to explode into smithereens. He had destroyed the Strider, but there was no evidence of it there. He later found out, if he took one of those  mines in his gravity gun the train would never leave the station, in fact nothing would happen at all.

Half-Life 2: First Episode, from VALVe, just out June 1, 2006