Possible Clues:

• Tiny air sacs in the lungs
• Lung air sacs
• Tooth sockets
• Air sacs
• Bit of lung from bodies of calves, solid
• Parts of lungs I've all burst, inhaling oxygen
• Air cells in the lung
• Sockets for tooth roots
• "I'm ___. Think I'll take a little breather"
• Honeycomb cells