Question

Small mice fit nicely into coat pockets. Which word or group of words is the complete predicate?

Answer 1

Small mice fit nicely into coat pockets.

The complete predicate in this sentence is "fit nicely into coat pockets."

This is because a sentence is made up of two halves: the complete subject and the complete predicate.  The latter of these two makes up the part of the sentence that describes the subject, or what the subject is doing.