How did Rainsford end up going overboard?

After Whitney retires to his quarters, Rainsford decides to stay above deck to smoke a pipe. He sits in the silent, dark night and looks out over the water. Suddenly, a sound startles him—the sound of a gun being fired. He quickly walks to the edge of the railing to try to get a better look at his surroundings. He is unable to see anything through the murky darkness. Rainsford accidentally knocks his pipe out of his mouth during his attempts to get a better view. In his attempt to catch it, he loses his balance and falls into the water.