Related Clues:

• First X or O
• Clown's sine qua non
• First O
• Odd habit
• A kind of twitch
• A little jerk?
• Something strange
• ''___ Tac Dough'' (game show)
• First 'O'?
• Fixation
• X or O, in a game
• Uncontrollable movement
• Habitual jerk
• Marx Brothers' forte
• "Space ___" ("Ground control to Major Tom" song)