The running joke about Walter not remembering Astrid's name is back with a vengeance. He calls her Astro, Aspirin and Astrix throughout this episode.
The glyphs for this episode spell out: EMPATH
Neil's safe combination is 7-9-3. Since Neil is a mathematician and highly religious (to the point of believing himself to be an Angel of Mercy on Earth), this is not surprising, as all three numbers are considered divine numbers in most major religions of the world.
The car that Olivia drives is a Nissan Leaf which is an Electric Car. When Peter and Olivia arrive at the cabin at Reiden Lake you can hear a gasoline combustion engine meaning the sound effects people played the wrong sound for the engine.
When Astrid speaks to Walter through the monitor device, Walter says "Kirk out"! as he hangs up. Leonard Nimoy plays William Bell in Fringe and Spock in Star Trek.