Related Clues:

• Idiosyncrasy
• Quirk of behavior
• Unconscious quirk
• Start of a simple game
• First X, maybe
• Sudden contraction
• Sign of nerves
• Muscle contraction
• Twinge
• Muscle problem
• Involuntary twitch
• Recurrent twitch
• Swimmer's bane
• Eccentricity
• An X could represent it