After the butterfly mutation Walter says: a friend of mine once said that "Any sufficiently advanced technology is indistinguishable from magic". This is a famous quote of science fiction writer Arthur C. Clarke.
The glyphs for this episode spell out: MUTATE
Walter sings and hums a melody (he can't remember the name) throughout the episode that is from the opera Carmen by Georges Bizet. It's one of the melodies from the Toreador piece.
The title of this episode "Johari Window" refers to a cognitive psychology tool used primarily in the United States to help individuals better understand their relationship with themselves and others. This epitomises the plot of the episode perfectly.
You can see the Observer in the background the moment Rose comes into the shot to call the sheriff out at the town "meeting".