Shawn and Gus sneak into old man Fuller's house to snoop through his attic. In the very next scene, both characters are wearing completely different outfits, even though the two had simply come down the stairs and walked across the street.
In this episode Gus tells his parents that even though he is 29 he knows that they have only been married for 28 making it seem like they got married when he was on the way. In the next season Christmas episode though he has an older sister named Joy.
When Gus' father hands Shawn some money to watch after Gus, it is initially a partially folded $50 bill with the face facing down. It then changes to a $20 folded differently, and then changes again.
Position of Mrs. Guster's hands when she is custody at the police station.
Juliet O'Hara states that her family celebrates a traditional Scottish Christmas, yet the name O'Hara is of Irish origin, not Scottish. However, she lives in the United States, which is a cultural melting pot and therefore she may have Scottish ancestry in her background as well.
The Scottish festival of Hogmanay is traditionally celebrated on New Year's Eve, not Christmas. The "first-footer" is actually the first visitor of the New Year, and he/she brings a gift of coal, and the food part of the gift is traditionally "Black Bun" (a form of pound cake).