(at around 9 mins) Olivia and Peter see a 'Resist' poster with Henrietta'a picture. In the background you see two flyers for a missing child called Calla Dreyer. 'Calla Dreyer' is the head of Makeup for the Fringe series.
Once again, Walter cannot remember Astrid's name. Here, fresh from his acid trip in the previous episode, he calls her "Acid".
The coded glyphs at the commercial breaks spell out SENSE.
When the Observers are searching September's apartment, a surveillance device placed above a doorway can be seen blinking in the familiar Green-Green-Green-Red light pattern just before an explosion occurs.