Still Waters __; Look Beneath a Calm Exterior
Puzzle 3 of Look up Easy Pack
Question is: Still Waters __; Look Beneath a Calm Exterior
and the answer is: RUNDEEP
Word Meaning:
RUN DEEP — (informal, figuratively) Of a feeling, belief, or problem, to be very intense, serious, and firmly established, often existing for a long time.
Definitions from Wiktionary.