Mr White is said to have ‘smiled faintly’ when receiving the news of the compensation money for his son’s accidental death at work. The full sentence in which this phrase appears is given below:
Unconscious of his wife's shriek, the old man smiled faintly, put out his hands like a sightless man, and dropped, a senseless heap, to the floor.
Mr White, then, is utterly shocked, so much so that he passes out, and his wife screams aloud. They are shaken to the core not just by news of their son’s death but by the compensation sum that will be paid out to them. This sum is two hundred pounds, exactly what Mr White had wished for upon the monkey’s paw just the night before. This grim incident would appear to furnish proof of the paw’s diabolical powers, as hinted by Sergeant Major Morris.
There is an element of the blackest humour about the situation, which is probably why Mr White smiles. He is stunned by the way in which his wish has come true, so terribly unlike the usual fairytale ideas about wish-fulfilment.