Possible Clues:

• Impassive expression that hides one's true feelings
• *Gambler's stoic expression
• Impassive expression
• It's hard to read at a table
• Inscrutable expression assumed to conceal emotion
• Inscrutable person
• Emotionless look
• Feature of some bluffs
• You'll get nothing out of a good one
• Impassive expression (at the card table?)