If you recall from last episode (In the Beginning), Dean caught Sam literally exorcising a demon with the power of his mind. After watching Sam harness his powers and realizing that the woman he is with is Ruby, Dean angrily confronts his brother and demands that he stop doing this as it is dangerous. Sam had previously told Dean that he wasn’t utilizing this power and had kept it hidden from Dean for exactly this reason but with Ruby’s help he’d been tapping into the demon blood – blood that Sam now knows a lot more about thanks to his visit to the past and Castiel – and while Sam’s argument that he’s using this power for good sounds like it makes sense, anyone who’s read history (or comic books for that matter) knows that it’s a slippery slope.
After Dean explains to Sam more of what he’s learned about the nature of his power and the message from Castiel, Sam agrees (again) to not use his power but he obviously disagrees thinking that he can control it.
There are cannibals and then there are the Rougarou … The rougarou (alternatively spelled as roux-ga-roux, rugaroo, or rugaru) is a legendary creature in Laurentian French communities linked to European notions of the werewolf. The name in fact comes from two different french words – Loup (French for wolf) and garou (a man who transforms himself into an animal). Now we’ve seen werewolf’s before in Supernatural – the Wendigo in the 2nd episode – however in each of these cases, the creature has had some control over its actions. In this case however the Rougarou has no control and when Dean and Sam are called by another hunter to help solve a case in Carthage, Missouri they discover a man going through a painful process of transformation into one of these beasts.
During the hunt, Sam lashes out on Dean, saying he is tired of how Dean looks at him like a freak and while Dean’s initial plans to deal with the man are the same as normal – shoot first and deal with the consequences later – Sam needs to see if its possible for the man to be more than the blood in his veins. Sam wants to reason with him and explain what could happen to him and his family if he were to succumb but Dean believes that while regrettable he is doomed.
After a long conversation, they are able to persuade the man and he manages to take some control over his transformation, but unfortunately the hunter who initially contacted Dean and Sam chooses to take matters into his own hands and threatens the mans wife (& unborn child). This tips him over the edge and he completes his transformation killing the hunter in full view of his horrified wife who he manages to spare.
When the man tries to kill Dean, Sam is forced to kill him by burning him alive. Seeing what the man went through, Sam decides to stop using his powers.