Surprisingly enough, they don't immediately leap for each other's jugular, so we must endure an extremely chatty round of accusations and counter-accusations before they actually start kicking the crap out of each other. Dean goes first, for whatever reason, and long story short, the Sam he knew is gone, replaced by the remarkably broad-shouldered corpse-fucking LIAR he now sees before him. Sam's retort? Basically, that Dean came back from Hell a whiny little piece of shit who's worthless as a hunter, because he's spending all of his time in the bottom of a bottle feeling sorry for himself and all of those souls he tortured over the past forty years. "Boo. Hoo!" Sam snots, and then? It. Is. ON! "VIOLENCE!" Dean whips the hunting knife at Sam's head, and how he missed a target that large, I'll never know, but Sam manages to duck it in order to kick Dean's ass. Yep, for once in his miserable life, Adult Sam fails to suh-huuuuuuck at the hand-to-hand, and the results are glorious indeed as he slugs and punches and whacks and thwaps and bomps and stomps and slams Dean's stumpy little ass from one end of the room to the other, until they end up where they started at the front door. "UNREPENTANT ACTS OF WANTON VIOLENCE!" Unfortunately for Sam, Dean manages to flip him around so his back's against the door, and then Dean -- with the last of his strength -- charges, hitting Sam so hard that the door blasts off its hinges, and they both end up on the floor outside, Sam far more winded by the experience than Dean.
Dean next smashes some glass to yank a fire axe from its nook in the wall, and he's about to split Darling Sammy's skull in two with the blade when... Bobby shows up out of nowhere to save the day? Okay, we'll go with that. But only because Bobby is so awesome. Yep, Bobby appears from nowhere to yank the axe from Dean's hands while at the same time jamming a bronze dagger into Dean's shoulder. "No!" Sam shouts from the floor, still creepily and eternally devoted to The Siren, but Bobby has no time for that sort of crap, and flings the dagger end over end into The Siren's back. The Siren falls against a cigarette machine mirror, staring at his own hideous reflection one last time as his own poison works its way through his body, before dropping the rest of the way to the tacky, threadbare carpeting, dead. The effects of The Siren's venom slowly drain away, and Our Intrepid Heroes are left gaping at each other in shock as the METAL TEETH CHOMP! arrives to drag everyone away into the final commercial break.