Continuity mistake: When Gus takes the Doritos bag from Shawn and sits down, every time the camera is behind Gus, the back of the bag is facing the camera, and when the camera is in front of Gus the back of the bag is also facing the camera. When Shawn stands up the bag is suddenly between Gus' legs.
Continuity mistake: When Shawn flashes back to remember where he has seen Pierre Desperaux, he flashes on a photo of Pierre in Lassie's apartment next to Ernesto Chavez (on the right) on Lassie's wall. Going back to Season 3, Episode 11, when in Lassie's apartment, there is no photo next to Ernesto's photo.
Character mistake: When Shawn is checking Ed's book of valuables, the crown that Shawn thinks Despereaux will steal, has a listed value of "950,000 - 1,000,00,000 USD." I guess it's really, really(!) valuable, enough that a whole new numbering system was made up for it.