"Yeah? You figured out how to get back through that mirror without mercury poisoning at high velocity? You better be sharing details, man."

That's his way of calling B.S. on the Doctor. None of them are 'just passing through', they're all stuck, and the sooner he helps break this toothpick-in-a-suit of his denial, the better off everyone will be. No one likes a naysayer - he should know, he used to be the big one in his group.

"Seriously, though. Name your poison."