Walter refers to the killing of albinos in east Africa and the using of body parts in rituals. This is not imaginary. To the present day an occasional news report from the region refers to the murder of an albino for such reasons.
The glyphs for this episode spell out: DAVID
Walter is using the same mouse maze that Faraday used in Lost. Both shows were created by J.J. Abrams.
When Walter shows Olivia and Lincoln the octopus, he references the Beatles song: Octopus's Garden.