Over-inquisitive dog drawn into boxes (6)
I believe the answer is:
snoopy
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for snoopy that I've seen before include "Inquisitive; cartoon dog" , "Curious" , "Cartoon character" , "Charlie Brown's cartoon dog" , "Prying, as in Peanuts" .)