Related Clues:

• ''Boo!'' accompanier
• Emulate a snake
• Tire leak sound
• Sound issued with an arched back, perhaps
• Radiator or kettle sound
• Let off a little steam
• Sound from a snake pit
• Air-leak sound
• Sound of crowd disapproval
• "Boo" accompaniment
• What's missing from the theme entries
• Asp's greeting
• Sound from a leaky tire
• "Boo" follower
• [I can't believe you just stepped on my tail. Now back the fuck away.]