He's ready to pull the cloth down again but the more Dean talks the more Doc sort of does a squinty triple take, unable to completely take his eyes off the covering but also unable to completely take his eyes off Dean.

"So I pull this off and say... my secrets three times? And she will climb out of the mirror and claw my eyes out. While you dispatch of her." Is that the plan? "Any... secret in particular? Are you sure you don't need a weapon?"