Lethe (Λήθη) in Greek mythology is the river of forgetfulness. It is one of the five rivers flowing into the Hades, the Underworld; drinking its waters causes the drinker to forget. It is also the name of the Goddess of forgetfulness.
Sodium Pentothal is a barbiturate used for anesthesia, and in small doses, as a "truth serum". It is identifiable by its strong odor of garlic and onions, which Shaw detected when she sniffed the syringe.
According to the PET computer, the episode takes place on Dec 17, 2013, the original airdate of the episode.
Root received the number instead of Finch, this indicates that Root has a way to communicate with the machine without the use of a telephone.
This episode is the first part of a two episode mini-arc; the POI and storyline of this episode carry over into the next episode, "Aletheia".
This episode includes the first appearance of Control. The alert viewer might have seen a red box appear around her when she exits the elevator during their escape the hospital. She only appears on screen for half a second.