When Sam is about to start preparing his salad shake in the diner, he places the plastic fork upside down between his teeth. In the close-up less than a second later, the fork is the other way up.
At the beginning of the episode where Gary/Sam is in the bar drinking the banana daiquiri, the levels of the beverage go up and down from scene to scene.
There are several "errors" exist that are typically found in body-switching-type episodes of this sort, but are unavoidable because of either dramatic necessity to make things clear to the audience (Sam's voice instead of Gary's being heard when Dean plays back his messages), the fact that ultimately these are actors performing roles (sight lines), or to avoid distracting the audience (clothing that fits regardless of body).
Dean: Wow, is it just me, or are we actually drinking together?
Gary/Sam: We don't do it that often, huh?
Dean: Yeah, you can say that.
Gary/Sam: Well, we should, You're a good guy, Dean.
Dean: Wow, you are drunk.
Sam: Gary, take it from someone who knows. Chill out, man. Your life ain't that bad.
Gary: Uh, you met my parents?
Sam: Yeah, so what? It's your life. You don't like their plan for you, tell them to cram it. Rebel a little bit. In a healthy, non-Satanic way.
Sam: I wish I had your life.
Gary: You do? Thanks.
Sam: Get on out of here.
Dean: That was a nice thing to say.
Sam: I totally lied. The kid's life sucked ass.
Music: Rock And Roll Never Forgets (Bob Seger)
UK: April 21, 2010 on LIVING
Sweden: July 16, 2010 on Kanal 5
Spain: November 8, 2010 on AXN
Australia: January 31, 2011 on ELEVEN
Germany: February 7, 2011 on Sky Cinema Hits
Czech Republic: September 23, 2011 on Prima COOL
Finland: May 22, 2012 on Sub
Dean: This whole Amityville thing being thrown at them.
Referencing the purportedly true-life story of the Lutzes, who moves into a house in Amityville, NY, and discovered that it was haunted. Jay Anson wrote a book relating the events, which became the target of lawsuits over its truthfulness. The book spawned a movie adaptation in 1979 and a series of sequels and remakes.
Sam: And the Freaky Friday crap?
Referencing the 1972 children's novel by Mary Rodgers, which tells the tale of a rebellious teenager who finds herself swapping bodies with her mother. The novel was subsequently adapted three different times into movies, in 1976, 1995, and 2003.
Dean: Welcome back, Kotter.
Referencing the 1975-79 TV series, which told the story of Gabe Kotter (Gabriel Kaplan), who returns to his old neighborhood to teach a remedial class consisting of the local gang, the Sweathogs.