Related Clues:

• Part of X-X-X
• See 36-Across
• Part of OOO
• Facial movement
• Sign of stress
• Game opener
• The first X?
• Part of a game win
• 'Hollywood Squares' square
• Tic-___-toe
• Spasm
• Idiosyncrasy
• Quirk of behavior
• Unconscious quirk
• Start of a simple game