Possible Clues:

• Not saying much, showing discretion about one vase
• Isn't saying much as Adam is consumed by diplomacy covering The Ashes
• Isn't saying much, as Adam is consumed by diplomacy covering The Ashes
• Withdrawn train cut for engineering work?
• Understood vase is rarely open
• Understood vessel is reserved
• The first to twitch curtain is weirdly antisocial
• Silent comic ain't curt
• Prowler back, I go quiet
• Quiet performer enthralling one in performance