I was taking some photos of a railroad bridge, when a heavy, long frieght rolled over it going about 45 MPH. The supports creaked and groaned, the wheels of the train were squealing and clanking, the metal part of the bridge right above my head was deflecting probably an inch or two to each side, and the timbers would occasionally jump a little off the ground. I remember thinking, "this sounds like the end of the world".