Related Clues:

• Stool pigeon
• One who sings
• Wharf pest
• Sewer resident
• Common test subject
• Muppet Rizzo, e.g.
• Plague carrier
• Dirty dog
• Nocturnal rodent
• Untrustworthy one
• Lab maze runner
• Untrustworthy sort
• It may be down in the dumps
• Snitch (on)
• Renegade