Related Clues:

• It could be represented by an "X"
• Physiological reaction
• Involuntary muscle contraction
• Muscle cramp
• Persistent personal quirk
• ___-tac-toe
• Big jerk
• First O?
• Sudden jerk
• Throe
• Writer's cramp, for example
• Flurry of activity
• Quirky behavior
• The first O of O-O-O
• Muscle woe