Possible Clues:

• Sting like ___
• Busy as
• '... sting like —'
• '... sting like '
• "Float like a butterfly, sting like ___"
• End of an Ali quip
• Last words of an Ali boast
• ''... sting like ---''
• Had ___ in one's bonnet (2 words)
• End of a Muhammad Ali motto