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.
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.
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.
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.
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.
Answer: It's Ashton Kutcher's dog.