Arthur has been nothing less than ramrod stiff since he's been separated from the other two. Because without them he has zero concept of where he is (besides the obvious, an interrogation room at the station), how long anything has been or even who or what is in the room with him.

When the door opens, he actually relaxes a fraction, just from the sheer fact he's not alone.

"What can I say, officer?" he returns, bitter and wry. "I've never taken well to my mind being toyed with."