Revealing mistake: The scene where Donna and Eric are running towards each other, each shot of Donna and Eric individually shows them running past the same umbrella and surfboard. They were using the same section of the beach to shoot both Eric and Donna running.
Continuity mistake: At the end of the episode "You Shook Me", Jackie is talking to a drunk Kitty who is putting mini umbrellas in Jackie's hair. The first shot of her doing this, she puts a green umbrella on the right side of Jackie's head. After Kitty asks for more umbrellas, the shot changes to Jackie which now has a pinkish, red umbrella on the right side and two green ones on the top.
Over the Hills and Far Away - S5-E6
Continuity mistake: When the girls go to Marquette the signs say 'GO GOLDEN EAGLES', however before the mid-1990's Marquette's nickname was 'the Warriors'.
Factual error: Kelso is wearing a t-shirt with Dirty Harry on it saying "Go Ahead, Make My Day". Sudden Impact was the first Dirty Harry movie to use that expression and that film didn't come out until 1983.
Continuity mistake: When Red and Eric were talking in the driveway there was a van right next to them. The tail lights shown on that particular model were only produced in the mid 80's and later.
Visible crew/equipment: As Donna plays footsie with Eric in the car while driving up to Jackie's ski lodge, a crew member's arm can be seen in the backseat. (00:05:17)
Answer: It's Ashton Kutcher's dog.