Man Overboard

My son Derek and his friend Casey, both five years old, were playing noisily in a large box in the basement.
I poked my head down the stairway and discovered they were pretending to be pirates sailing across the ocean.
Joining the fun, I started pushing them around the basement. When I decided it was time for a storm to hit, I rolled the box from side to side and made sounds of thunder. "Tie down the hatch! Man the lifeboats!" I yelled. Both boys were screaming with laughter. I increased the roll of the box. "I think we're going over! The boat's going down, every man for himself!" All of a sudden a terrified look appeared on Casey's face, and he began to cry. I stopped abruptly, thinking he might be hurt, and asked "Casey, what's the matter?" "I . . . I can't swim!"