Before Shadow reveals the wound the tree gave him, Wednesday begins to recite a poem from the source novel. It begins "I know a charm that can cure pain and sickness, and lift the grief from the heart of the grieving" and goes on to list eighteen such charms.
The song playing when the Vulcan factory is first shown is "Come on Get Happy" from The Partridge Family (1970).
Salim's role in the series is much larger than in the source novel. Originally, we don't see Salim again after his encounter with the Jinn. Later in the book, a reference is made to an Arabic cab driver being killed, suggesting that Salim is a casualty in the war between the gods.
The character of Vulcan was not in the source novel; he is a new addition to the TV adaptation. The character is based on the ancient Roman god of fire, the forge, and metalworking, but the inspiration for the new character did not come directly from ancient mythology. Instead, the idea came from a story that Neil Gaiman told showrunners Bryan Fuller and Michael Green about traveling through Birmingham, Alabama, and seeing the 56-foot-tall cast-iron statue of Vulcan that overlooks the city on Red Mountain. In an Entertainment Weekly interview, Green said that Gaiman was told that during Birmingham's heyday as a steel town, one steel mill had had a policy that it was cheaper for them to pay restitutional damages to the families of workers killed on the job rather than to pay to ensure their safety. The "torch" in Vulcan's hand would light up one of three colors to communicate the safety of the Mills - a green torch indicated that no employees had been injured during the previous 24 hours, a white torch indicated minor injuries and a red torch signaled there had been a fatality in the previous 24 hours. Green said that Gaiman characterized that policy as "as modern a definition of sacrifice as there might be".
Vulcan is the Roman god of the forge, and therefore weaponry, which in contemporary America means guns rather than swords. He is the Roman equivalent of the Greek Hephaestus.