Fringe Connections

The radioactive isotope compound from "The Cure" that caused heads to explode was used as a weapon against the Observers in "An Enemy of Fate".

When Nina looks in Bell's storage room for his copy of the First People book the camera pans by a copy of 'Dr. Spock's Baby and Childcare'.

A seahorse can be seen on Peter's luggage.

Ten Observers are present on Liberty island in "The Day We Died" from an assumed total of 12. One of the missing two Observers might be John Mosley, a potential former Observer, who was killed in "The Arrival". See the FAQs for more information (note: FAQs contain spoilers through season 5).

The green and yellow posters in the diner represent how this new timeline with the yellow/amber title sequence is starting to merge with the original timeline with the blue title sequence now that Peter has returned (blue + yellow = green).

The seahorse glyph can be seen as Olivia and Shapeshifter Charlie fight in the alley.

The ship at the end of "Nothing as it Seems" showed the creatures from "Snakehead".

Donald helped Walter set up the pocket universe hiding spot.

The butterfly glyph can be seen outside the entrance to the daycare center.

The Observers read Nina's phone call from the impressions her sound waves made on the glass in her office in "Anomaly XB-6783746", like Peter did in to hear the phone call Nancy Lewis made in "The Road Not Taken".

When Walter explains that his red/blue lensed glasses were created by his friend from Washington, Doctor Jacoby, he's referencing the television show 'Twin Peaks' which also had an eccentric man of science, Doctor Jacoby, who wore red/blue lensed glasses very similar to Walter's.

A seahorse can be seen hanging from the taxi when Walter listens to music.

The nanites in "Brave New World (Part 1)" have an "X" on them that matches the "X" on the shirt worn by the man Peter freed from Olivia's mind in "Lysergic Acid Diethylamide", suggesting that "Mr. X" from Olivia's mind may have been William Bell (who was ultimately behind the nanites).

All of the people in Olivia's mind wear blacks and greys because Cortexiphan subjects have a strong desire to blend in.

A seahorse can be seen in Walter's Monty Python trip.

Walter's password at Massive Dynamic in "Letters of Transit" is 0-5-2-0-1-0, the same as the combination to the Jacksonville daycare center and to Bell's safe in "Five-Twenty-Ten".

Jones said there are 10 tests for Olivia in total. The first was a box of lights that Olivia had to turn off with her mind.

The butterfly glyph can be seen as Olivia and Shapeshifter Charlie fight in the alley.

The tombstone in Olivia's dream state in "Pilot" says "He's Not Dead", possibly referring to John Scott, assumed dead, who appears at the end of "The Arrival".

Mark Young's colleague is wearing a butterfly pin, possibly prompting the subject of his hallucination.

The frog glyph can be seen as Olivia and Shapeshifter Charlie fight in the alley.

The bus in "The Ghost Network" was ambered. Huge sections of cities were ambered in the Redverse in "Over There (Part 2)".

The license plate on Olivia's SUV reads 1R2D21, and the licence plate on Broyles's SUV reads 1C3PO1.

A hand can be seen on the wall when Olivia and Peter attack the Observers and Loyalists.