A Very Supernatural Christmas - S3-E8
Continuity mistake: In 'A Very Supernatural Christmas' (S3E08), when the Gods are beginning to sacrifice Sam and Dean, they slice Sam's right forearm. However, at The End of the episode, Sam has his left forearm bandaged, not his right.
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.
Sierra1 ★