Related Clues:

• [Man, this is heavy!]
• Mournful cry
• Noble gas
• Incandescent lamp gas
• An inert gas
• Inert gas
• Fluorescent lamp filler
• Reaction to a bad pun
• Haunted house sound
• Light gas
• It often follows a pun
• Fluorescent tube gas
• About 1% of the Earth's atmosphere
• React to a pun
• Bad pun response