For anyone looking for it:

A party of potholers has imprudently allowed the fat man to lead them as they make their way out of the cave, and he gets stuck, trapping the others behind him. Obviously the right thing to do is to sit down and wait until the fat man grows thin; but philosophers have arranged that flood waters should be rising within the cave. Luckily (luckily?) the trapped party have with them a stick of dynamite with which they can blast the fat man out of the mouth of the cave. Either they use the dynamite or they drown. In one version the fat man, whose head is in the cave, will drown with them; in the other he will be rescued in due course. Problem: may they use the dynamite or not?