Related Clues:

• First X, in a common game
• It can precede or follow tac
• Eye twitch, maybe
• Twitch, regularly observed?
• A convulsive muscular twitch
• Knee-jerk response
• The first 'O' of O-O-O
• Twitch seen regularly
• Irregular movement with sign of approval reportedly
• Hearing blood-sucking arachnid, it might be nervous
• Automatic reaction of so-called dog biting some footballers
• Idiosyncratic behavior
• Twitch at odd points?
• Nervous symptom
• Facial twitch, say