Soldier Boy performing Roaring Lion's "From a Logical Point of View" was inspired by Robert Mitchum's 1957 album "Calypso - Is Like So". Showrunner Eric Kripke has the album cover framed on his office wall.
Black Noir is shown preparing to eat cold baked beans, which is a strange behaviour also done by Rorschach of the Watchmen.
Beware that there is a special end-credit scene, wherein an unseen audience applauds as the animated cast members join hands to take a theatrical bow.
When Soldier Boy insists to Hughie that he doesn't have "shell shock", he's referring to the World War One era term for Post-Traumatic Stress Disorder before the condition was studied more thoroughly by psychologists. Over the years the condition has been referred to as "battle fatigue", "combat fatigue" and "operational exhaustion".
The producer is making fun of Soldier Boy's singing when in reality, the actor who plays Soldier Boy, Jensen Ackles, is a professional musician and singer.