R-R-R-G-H-R-O-R-R-H-F-F," exclaimed the watchdog as he dashed up to the car, loudly puffing and panting.
Milo's eyes opened wide, for there in front of him was a large dog with a perfectly normal head, four feet, and a tail--and the body of a loudly ticking alarm clock.
What type of wordplay does the author use in the passage?
a. homophone
b. idiom
c. onomatopoeia
d. pun