"two inmates are trying to escape a mental institution. They are trying to work out how to get over to the next building, outside the institution, one inmate leaps across, but the second is afraid of falling. The first says "I'll turn on this flashlight, and you can walk along the beam of light to get across." The second inmate replies, "What are you, crazy? I'm not falling for that; you'll turn the flashlight off when I'm halfway across."