Who Are You - S6-E15
Factual error: In this episode, when Donna and Jackie are arguing about who is going to go outside, Jackie is seen holding a box of Chips Ahoy cookies. The logo seen on the box was used in the late 90s and early 2000s, rather that the logo used in the 1970s. (00:17:30)
Continuity mistake: After Eric's mishap with Donna's wedding dress, Kelso is in the Forman's driveway with the canoe (yes, a canoe), and the scarf around Kelso's neck changes repeatedly.
Won't Get Fooled Again - S6-E13
Continuity mistake: When Eric bursts into the kitchen to tell Kitty and Red, who are sitting at the table, that Donna is not pregnant, the items on the table change position depending on the angle of the shots.
Continuity mistake: When Eric and Hyde are speaking while sitting on the couch, Eric's left leg is either over his right leg or under it, depending on the camera angle.
Revealing mistake: When Fez and Suzy first meet, they do "12345 you owe me a coke" you can see Kelso mouthing the same line as well. (00:08:04)
Squeezebox - S6-E20
Continuity mistake: Kelso gets really close to Eric when he's trying to burn him about the other girl. The shot changes, and Kelso is further away.
We're Not Gonna Take It - S6-E6
Visible crew/equipment: The edge of the camera lens is visible throughout this episode. It's also known as vignetting.
We're Not Gonna Take It - S6-E6
Continuity mistake: When Eric is carrying the tray and they're trying to get him to drop it, he hops over a chair. The tray rotates between cuts. Look at the glasses.
Character mistake: As the little boys are trying to get a peek at Donna's breasts, you see more and more of them. The first two times, you can't see them. The final time, you can see a kid or two far left. They're having trouble standing still. When it cuts to a wider shot, the kids come from behind the wall to see Donna. Chances are, since the aspect ratio was intended for 4:3 TVs, they didn't intend for the kids to be visible.
Answer: It's Ashton Kutcher's dog.