Dean: You kidding? You still keep in touch with your college buddies?
Sam: Why not?
Dean: Well, what exactly do you tell them? You know, about where you've been? What you've been doing?
Sam: I tell them that I'm on a road trip with my big brother. I tell them I needed some time off after Jess.
Dean: Oh, so you lie to them?
Sam: No. I just don't tell them... everything.
Dean: Yeah... that's, that's called lying. Hey man, I get it. Telling them the truth is far worse.
Dean: Look, it sucks. But with a job like this you can't get close to people. Period.
Sam: You're kind of anti-social, you know that?
Dean: Yeah, whatever.
Sam: Hey, Bec, can we take those beers now?
Rebecca: Uh, sure.
Sam: Hey, ah, maybe some sandwiches, too?
Rebecca: What do you think this is, Hooters?
Dean: (quietly) I wish.
Dean: I think we're close to its lair.
Sam: Why do you say that?
Dean: Because there's another puke-inducing pile next to your face.
Sam: Ugh, gah!
Shape-shifter Dean: He's sure got issues with you. You got to go to college. He had to stay home. I mean, I had to stay home, with Dad. You don't think I had dreams of my own? But Dad needed me. Where the hell were you?
Sam: Where is my brother?
Shape-shifter Dean: I'm your brother. See, deep down, I'm just jealous. You've got friends, you could have a life. Me? I know I'm a freak. And sooner or later, everybody's gonna leave me.
Sam: What are you talking about?
Shape-Shifter Dean: You left. Hell, I did everything Dad asked me to and he ditched me, too. No explanation, no nothing, just poof! Left me with your sorry ass. But still, this life... it's not without its perks. I meet the nicest people! Like little Becky. You know... Dean would bang her if he had the chance. Let's see what happens.
Dean: That better be you, Sam, and not that freak of nature!
Sam: Yeah, it's me. He went to Rebecca's, looking like you.
Dean: Well, he's not stupid. He picked the handsome one.
Rebecca: Okay, so this thing, it can make itself look like anybody?
Shape-shifter Dean: That's right.
Rebecca: Well, what is it? Like a genetic freak?
Shape-shifter Dean: Maybe...evolution is about mutation, right? So maybe this thing was born Human but was different, hideous and hated... until he learned to become someone else.
Dean: (about his doppelganger) All right, but first I want to find that handsome devil and kick the holy crap out of him!
Sam: What are you gonna do to me?
Shape-shifter Dean: I'm not gonna do anything, Dean will, though.
Sam: You'll never catch him.
Shape-shifter Dean: Oh, it doesn't matter. Murder in the first? Of his own brother? He'll be hunted the rest of his life.
Dean: I really wish things could be different, you know, I wish you could just be Joe College.
Sam: Nah, that's okay. You know, truth is, even at Stanford, deep down, I never really fit in.
Dean: Well, that's 'cause you're a freak.
Sam: Yeah, thanks.
Dean: Well I'm a freak, too. I'm right there with you, all the way.
The e-mail from Becky is dated December 5th, but it is later established that this episode took place in March.
When Sam and Dean enter the sewer, it's light outside. But when they come out of the sewer a minute later, its dark.
During the episode, it is light at 5:30 in the morning. Since this episode is said to take place in March, the typical March sunrise in St. Louis is at 6:30 am, so it shouldn't have been light outside at 5:30.
During the scene where Sam is fighting the Skinwalker at Rebecca's place, the Skinwalker places its knife on a pool table. Sam flips up the knife to cut the rope off of his hands, and during this shot we see that his feet are tied together as well. However, in the next shot his feet are free without him using the knife to cut the rope away.
In the opening scene, Sam is checking his email and a microphone can be seen taped to the dashboard in front of him.
Derived from the German word for look-alike (Doppelgänger), the word often refers to an "evil twin". This episode ties in closely to the Doppelganger term, mainly when the Shapeshifter takes control of Dean's body. Also related to the term, in several mythologies, seeing one's doppeldaganger is a death omen. Though Dean was not killed, his evil twin goes on a killing spree.
This episode focuses on Shapeshifters and Doppelgangers. One of the most common and popular shapeshifters/doppelgangers is the werewolf, as seen in this episodes. Traditionally, werewolves are humans that have the ability to shapeshift into a wolf.