Related Clues:

• It has a bigger brain than a mouse
• Squeaking rodent
• Dumpster explorer
• Cluny the Scourge in "Redwall," e.g
• Mouse's
• Urban scourge
• Rodent in a subway tunnel
• Animal studied in a Skinner box
• Rodent in some zodiacs
• It's caught in letters 3-6 of 36-Down
• Animal that's a real gnaw-it-all?