See, Walter clearly slipped him the good stuff. Because this particular hallucination was far too Sam-like for his own good. When Walter opened the door, he gave him a smile.

"Hello, Agent Winchester," Walter nodded, returning the smile. "Is something wrong?"

"Walter -- did you happen to slip me something? Again?"

Walter looked confused -- it was a look that Dean saw often. "No, no of course not. You specifically told me not to after the plane incident."

Dean paused, considering that for a moment, before pointing back over his shoulder with one hand while the other took stock of the situation. No gun, no knife, but Peter's shoulder holster was hanging in the doorway of the room. "Is there a freakishly large man standing behind me?"

"Yes, of course, though I wouldn't say freakishly so. I met a man once who loomed at about eight feet tall. He was rather impressive," Walter said with a wide smile as he waved back at Sam. "But your friend seems very nice."

"Uh-huh," Dean replied, reaching forward into the room to pick up the piece, before nodding back to Walter. "Sorry to have bothered you. Go back to bed."

Walter nodded, even if he looked concerned. Once the door closed, Dean turned around and pointed the gun evenly at the thing pretending to be his brother. "Don't say a word. Go back in the room."