Shawn says that he and Gus have bathed together before, to which Gus replies that it was when they were three. However it was established in an earlier episode that they met and became best friends when they were five.
When Dr. Reidman appears at the Psych office to collect Shawn's DNA, Shawn says "Well you're in luck. I just drank a liter of Teas' Tea." However, DNA is not found in urine.
At the beginning, Shawn and Gus are walking along the beach, and Juliet shows up. She complains of an odd smell, and Shawn throw his corn nuts (the source of the smell) behind him. Later, in the hospital, Gus finds the corn nuts in Shawn's sweatshirt while wearing the hazmat suits. Unless it's assumed Shawn picked them up, or got new corn nuts, they shouldn't have ended up in his sweatshirt pocket.
Sean throws his burrito not the corn nuts. This is incorrectly regarded as a goof.
When Shawn is talking to Juliet on the phone while in the hotel room he pulls the phone away from his ear and you can clearly see the screen indicating that he is not on a call. He then places the phone back to his ear and continues his conversation.
Gus asks Dr. Reidman whether he refers to the virus in the feminine tense. "Feminine" is not actually a tense, since tenses express time references.
At the beginning when Henry is getting rid of Shawns lice he hoses Shawns head down and there is heat coming out of Shawn's head right afterward which a hose would not give out.
At around 18 minutes in, Dr. Reidman says that a person has to "come in contact with an infected person's secretions" in order to be infected with the virus. When Shaun, Gus, and Juliet stop Dr. Mallon in the hospital, he's been sweating a lot (there are stains on his shirt, and what look like sweat coming off his shoes in the earlier flashback). Sweat is a secretion, yet Shaun takes the cooler from him barehanded, and no one quarantines him again.