The glyphs for this episode spell out: SWITCH
The Observer is briefly seen as Walternate returns to Bishop Dynamic.
When Walter is trying to activate Olivia's ability to cross over he gives her a puzzle. This puzzle was used in JJ Abrams show Alias. It was a tool used when training children to be sleeper agents for the CIA
The computers on many of the desks of Walter's Florida office appear to be Commodore PET 2001 systems. This was a personal computer introduced in 1977 and had a 1Mhz 6502 processor. It sold for $795 at the time.
The timeline of this episode contradicts previous episodes that suggest Olivia was three and living in Jacksonville with her father at the time of the Cortexiphan trials. The room where Olivia starts a fire is also different, and the burn marks leave a circle in the middle of the room rather than an untouched corner.