When Isabella stood on a wooden crate to peek in through the window of the boathouse, there was a wooden railing behind her at the edge of the deck. When she fell backwards off the crate, she fell in the water, proving (a) that the deck had become much narrower, since she couldn't simply step back to avoid falling, and the railing wasn't there. But the lower rail was still there when Isabella surfaced. How could she have fallen in the water?