The line ''words died away on his lips'' is a personification.
EXPLANATION:
The moral of the story in 'The Monkey's Paw' is that one should not interfere in their fate. We should be careful about what we wish for as it might come true. Personification means that human qualities are assigned to objects or animals.
Words cannot die, but the author wants to say that his words had no meaning, or he had nothing to say and thus depicts this line making a personification.