I thought it was curious that a crossroads demon showed up in this episode about demon deals and the road that leads you to becoming a demon.

All Hell Breaks Loose II: the RED                    v    The Red-Headed Demon

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And then more and more references to Dean’s initial demon deal (his father’s son) and the effect it had on his humanity cropped up.

All Hell Breaks Loose II:  "It’s a fire sale, and everything must go.“

Executioner’s Song: "It’s a fire sale, and everyone must go.”

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Long Distance Call: “I’m scared, Sam”   Executioner’s Song: “I’m scared, Sam”

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No Rest for the Wicked: “If we go down then, we go down swinging.”

Halt & Catch Fire: “And when all is said and done, I’ll go down swinging.”

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No Rest for the Wicked                        v            Executioner’s Song

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On the Head of a Pin:  "You ask me to open that door and walk through it, you will not like what walks out.“

Executioner’s Song: "Plus, I need you three out here total out whatever comes out of there.  And I’m serious.  I mean whatever comes out. ”

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Alistair and Cain taking credit for what they’ve passed on to Dean.

On the Head of a Pin: “I carved you into a new animal, Dean.  There is no going back”

Executioner’s Song: “At a loss for words, my son?”

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The setting of the confrontation: note the two sources of light and devil’s trap

On the Head of a Pin                       v             Executioner’s Song

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All reinforcing that Dean’s execution of Cain can only take him further down that journey of losing his humanity.