Related Clues:

• Pressure cooker sound
• Vocal thumbs down
• Sign of a leak
• Boo accompanier
• Theater jeer
• Boo companion
• Moccasin sound
• Sign of an escape?
• ''Boo!'' accompanier
• Emulate a snake
• Tire leak sound
• Sound issued with an arched back, perhaps
• Let off a little steam
• Sound of crowd disapproval
• "Boo" accompaniment