Ben growled at the man who parked too close to his car. he was always guarding his prized possession. don’t get too close or he might bite!
which figure of speech, or literary device, does the author use in the passage?

I would like to believe that the figure of speech being used here is an idiom.

An idiom is a word or phrase which cannot be taken literally. Here, we see that the man is being compared to a dog and that he 'might bite'. The man will not really bite whoever gets close to the car, but he will get very upset!