In the beginning scene, when the young girl is with the vampire at the bar, the vamp calls her Kristen, and later in the ally, she calls him Robert. This is a reference to the vampire-human couple in the Twilight (2008) movies, played by Kristen Stewart and Robert Pattinson.
In the opening scene in the bar many of the bar patrons are drinking dead guy ale from rogue brewing company based out of Newport oregon. The show has shown previous bottles of beer in previous episodes, but they appear to be made up beers.
The term Twihard from the title of the episode is fandom slang blending the words twilight and diehard. It describes an avid fan of Stephenie Meyer's Twilight book series or the related films. The Urban Dictionary describes Twihards as stupid obsessive people (mostly teenage girls) who are in love with fictional characters.
The trivia items below may give away important plot points.
In an early scene, Sam and Dean are searching the bedroom of the latest missing girl. Dean is disturbed by the cover of a book which shows a man standing in a dark bedroom watching a young woman sleep. Later, after being turned by a vampire, Dean goes to Lisa's house to tell her goodbye. Fighting the vampire impulses, he is watching Lisa sleep in her bedroom in a manner eerily similar to the book cover that bothered him earlier.