The glyphs for this episode spell out: ENERGY
When Diane Kruger's character tries to remember someone's name on the telephone, she asks "Gorlami?". The character Aldo Raine uses this name as an alias in Inglourious Basterds (2009), also starring Kruger.
The Observer crosses the street in front of Miranda Green's car, just before she dies of cancerous tumors.
The episode's title references the mystery board game "Clue" in which players must determine who had killed Dr. Black, in what room and with what weapon. Clue is the game that Sam brings to Olivia's apartment to play with her in the middle of the night. This reference was also foreshadowed during the previous episode: when two of of the observers go to see the movie Back to the Future (1985), there is also a poster for the movie Clue (1985) hanging at the theater.
Walter shines an ultraviolet light on the cancer riddled arm and says the older tumors will refract a different color; indeed the tumorous handprint glows red. Refraction is the bending of light; the hot air above a black surface in summer bends light and gives us wriggly, heat roil images. When something absorbs UV light and subsequently glows a different color than UV it is called fluorescence.