At about 20 minutes into the show, Chloe Sullivan displays an aerial photo of Metropolis on a computer monitor. The aerial photo is actually of the south side of Chicago Illinois.
Clark is puzzled at how Hamilton is going to extract a sample of his blood. This is strange, since in "Phoenix", he personally provided a sample by cutting his arm with a sharp piece of kryptonite. Also, the negative effects on Clark appeared much weaker that time, so it's unclear why the same method wasn't used again instead of actually injecting him with the dangerous substance.
Jody Thompson appears as a police officer who makes out with Oliver. She also appeared as Gia in Season Five's "Fade", where she kissed Clark.
Oliver makes a reference to the video game series Resident Evil when he says "I was looking for Tess when the whole building went Resident Evil." This episode is very similar to the video game and film series Resident Evil, in which a virus that turns people into zombies is created by an evil corporation, known as the Umbrella Corporation, and is released into Raccoon City. The very beginning of the episode plays out like Resident Evil (2002), where Alice leaves the facility of the Umbrella Corporation to see deserted streets and a crazy evident zombie apocalypse.
Lois's outfit is similar to Jill Valentine's outfit in Resident Evil 3. Mainly the blue top and the black knee high boots.