Sam looks up and asks Dean if he knows of any shape-shifters that can fly, because the trail he picked up behind both Zach Guzman's and Fancypants's houses just abruptly ends. Dean says he doesn't know of any flying shape-shifters, and then wins the Nobel Prize of this episode (awarded for the exhibition of sentience) by proposing to Sam that the being could also have gone "down." The boys look down at a steaming manhole. Heh. Hot.
Cut to the brothers descending into a sewer tunnel. Not hot. Sam is excited by the probability that the tunnel runs under both crime scenes. Dean wanders over two feet, and calls Sam over. They kneel, and the camera pans down to show a truly horrific pile of bloody human tissue, with what looks to be a human ear lying in the foreground. Dean uses a knife to scoop up a slimy strand of skin or hair or both, and says he "just had a sick thought. Maybe when the shape-shifter changes shape, it sheds." He thwaps the slimy strand back into the pile and ewwwwww.
Cut back above ground, away from piles of tissue, which is generally where I like to be. Dean says that one thing he learned from Dad (besides jackassery?) is that there's one way to kill a shape-shifter. Sam provides the line "Silver bullet to the heart" as Dean loads a gun with said ammo. Sam's cell rings, and we cut to Blondie, who starts bitching at Sam, telling him she doesn't need their help anymore. She mentioned to her lawyer that they went to the crime scene, and her lawyer checked Dean's police-officer story and found it, well, wanting. Blondie hangs up on Sam. Sam mopes against the car, and Dean rides his big Gavel of Morality up to his brother to lecture him about lying to his friends. Dean tells Sam that they aren't like other people, implying that his brother just needs to cut off contact from his friends. Then he tries to comfort Sam by noting that "this whole gig? It ain't without it's perks" while handing Sam a gun. Oh, boys, with their antisociality and gun-brandishing.
Back in the sewers, where I don't want to be. The boys and their flashlights, lots of plinking and dripping and gummy-smacky shoe noises. They swing around a corner and slow down next to some sort of large pipe. Dean says he thinks they're close to its lair. Sam asks why. "Because there's another puke-inducing pile next to your face." Hee. Sam jerks his head back, "Oh...gaaahhh," as we get a nice little shot of the pipe coated in slimy pink tissue. Dean moves his flashlight beam across another pile of skin and body parts, lying amongst a pair of jeans and shoes. Sam bemoans how many murders this thing has committed, and turns toward Dean to discuss further nasty tissue-related things when right behind Dean, a figure with MS Paint eyes is lurking. Sam yells "DEAN!" just as the latter gets whacked across the face by the shape-shifter, who, by the way, has chosen to take the form of a young man with good hair and lovely chiseled cheekbones. At least the thing has some taste. The thing turns and runs; Sam fires after it to no avail. Dean moans and groans and holds his arm, which is weird because it looked to me like he got smacked across the face. If he did not get smacked across the face, that just goes to show that this shape-shifter really DOES have good taste in men.