Personification

A figure of speech that gives human qualities to objects, animals, or ideas.

Example From Text

And when, released, he sprang to his feet, his mouth laughing, his eyes eloquent, his throat vibrant with unuttered sound, and in that fashion remained without movement, John Thornton would reverently exclaim, "God! you can all but speak!"

Explanation

Can a mouth really laugh? Here, Jack London gives a mouth the human quality of laughing. The author uses personification to describe how happy John Thornton makes Buck.