Related Clues:

• 'Shut up!' ... or a phonetic hint to this puzzle's theme
• It may precede 'Don't let anyone hear!'
• "No whispering!"
• Library reminder
• Silencing sound
• "Stifle yourself!"
• "Quiet, please!"
• 'Zip it up!'
• Librarian's reprimand
• ''Keep it down!''
• Finger-to-lips syllable
• 'Hush up!'
• 'Button your lip!'
• ''Silence!''
• "Be quiet!"