When Nina opens the safe, she removes a toy car. She then replaces the toy, which lands upside-down, and removes some photographs. When she reaches into the safe to replace the photographs and remove a book, the toy is right-side up again.
When Walter mentions "Wooster," he is actually referring to the Ohio city, not the Massachusetts town of Worcester, which is pronounced similarly. In previous episodes, it had been established that a second set of Cortexiphan trials had been conducted in Wooster, Ohio.
When Nina Sharp is examining the "First People" books, the one in Hebrew is shown opening on the right side. Hebrew books open from the left side.
When Nina Sharp is examining William Bell's old office during the episode's opening scene, she touches Bell's framed Master's degree in "Abnormal Psychology" from Yale. The text is clearly written in English; Yale's undergraduate and graduate degree certificates are written in Latin, not English.
When Walter notices the blue Volkswagen Beetle passing by in the background, its engine sounds like that of an average car, rather than the distinctive sound of a Volkswagen engine.
Aaron Downey is presented as a Marine Corps Officer. However, in his picture, he is shown wearing an enlisted Marine uniform.