Related Clues:

• First X or O, say
• Bad liar's giveaway
• Mannerism or spasm
• Nervous movement
• Personality quirk
• "___-Tac-Dough"
• First O, say
• -- Tac
• A facial twitch
• Spasmodic twitch
• Muscular spasm
• Twitch in anticipation
• Twitch in analytical way
• A twitch of anticipation
• Oddity