Easter egg: On Disc 6, go to the Bonus Features section. Scroll down to the second option, and the light in the cabin on the right hand corner of the screen goes on. Click on it and you'll find a surprise.
Easter egg: On Disc 6, go to the Bonus Features section. Scroll down to the gag reel (the third item) and Dean's eyes in the shot on the left turn yellow - like the Yellow-Eyed Demon. Click on them for a surprise.
Answer: Over the next few episodes, it is revealed that something is not quite right with Sam - that his soul is missing since he returned from Hell, and he does not feel any emotion or attachment to his brother.
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