The opening title sequence that replaces the shattering glass is a replica of The X-Files (1993), another similar series about two FBI agents who investigate bizarre and potentially extra-terrestrial/supernatural cases, with the black lettering against the grey background and the phrase "The Truth Is In Here" at the end of the sequence, while The X-Files' read "The Truth Is Out There." Not only has Supernatural drawn numerous comparisons to the series, this episode is about the Winchesters battling what they initially think are aliens, and Mitch Pileggi has a recurring role in this series beginning this season. Pileggi also had a recurring role on The X-Files as Agents Mulder & Scully's superior, Walter Skinner.
After the encounter, Dean is being stalked by a burly man in a bright red cap. In Irish and English folklore, Redcaps (usually portrayed as ugly humans wearing red caps or hats) are malicious beings, typically acting as enforcers for the fair folk court (what said character essentially does) or simply harassing humans for their own entertainment.
At a convention Jared Padalecki had said that he felt it strange Sam had the salt all along and didn't think to use it, so after pouring the salt he ad-libbed the line, "Why didn't I do that before?"
The line "Fight the fairies!" is another X-Files reference as the first The X Files (1998) movie was called "Fight The Future".