When Juliet asks Shawn if he told Gus about their relationship he says that would be like putting it on his Facebook page if he had one, thus implying he doesn't have one. However he has previously mentioned that he has a Facebook page and that he keeps it open for public viewing so that prospective clients can check them out.
When Shawn shoots Carol, the gun he uses is a light gun, it's connected with one of those electric cables with metal protection, so there would come nothing out of the gun.
At around 18:50, as Shawn and Juliet are walking through Scare Fest, a Pizza Pizza sign is visible on the roller coaster in the background. Pizza Pizza is a Canadian-only pizza chain.
Ken says that he told Shawn last time (Romeo and Juliet and Juliet) that he only speaks six words in Chinese. However, he actually said in that episode that he speaks nine words in Chinese and six of those are numbers.