Related Clues:

• S-s-snake's s-s-sound?
• Sound of serpent
• Make snake-like noise
• (Make noise to) express disapproval
• Sound of snake
• What letting off steam might result in
• Hardly a sign of support
• Make snake sounds
• Boo mate
• Lip from crawler perhaps lets off steam
• Sound from an cat with an arched back
• Audible reproof
• [You smell like some other cat and I don't like you]
• Boo accompaniment
• Kettle emission