Tom felt his head buzz round, and he passed his hand over his forehead and through his curly yellow hair to steady himself.

He felt a frenzied impulse as he sat down to inform the examiners that he knew very well what they were going to ask him, and that it was hopeless for him to attempt to answer it.
The leading professor was a ruddy-faced, benevolent old gentleman, with spectacles and a kindly manner.

He made a few commonplace remarks to his colleagues with the good-natured intention of giving the confused-looking student before him time to compose himself.
Then, turning blandly towards him, he said in the mildest of tones-- "Have you ever rowed in a pond ?" Tom acknowledged that he had.
"Perhaps, on those occasions," the examiner continued, "you may have chanced to touch the mud at the bottom with your oar." Tom agreed that it was possible.
"In that case you may have observed that a large bubble, or a succession of them has risen from the bottom to the surface.

Now, of what gas was that bubble composed ?" The unhappy student, with the one idea always fermenting on his brain, felt that the worst had come upon him.

Without a moment's hesitation or thought he expressed his conviction that the compound was cacodyl.
Never did two men look more surprised, and never did two generally grave _savants_ laugh more heartily than did the two examiners when they realized what the candidate had answered.