The One With Rachel's Date - S8-E5
Revealing mistake: In the scene in the coffee house, Phoebe is talking to Monica who is drinking a cup of coffee. Towards the end of the scene, the camera is on Phoebe who is smiling and laughing at Monica. In the right-hand corner is a side view of 'Monica'; however, it is not Courteney Cox in the scene but a completely different actress. [Widescreen version only, although the "wrong" nose is visible in the original]. (00:06:20)
Revealing mistake: When he's attacked in Down Below, Dr. Franklin is shoved against a station bulkhead/wall that wobbles when he hits it. (00:15:30)
Sins of the Fathers Chapter 1: Doctor Strange - S3-E1
Revealing mistake: When Mary Jane and the other servants of Baron Mordo are flying through the city, they literally disappear into thin air. Probably a problem with rendering the 2D animation within the 3D animation. (00:01:00)
Homeless for the Holidays - S3-E10
Revealing mistake: When Mark goes to treat his cut, he leaves the lounge with a couple of tissues held to his head. He gets some supplies and puts a supposedly fresh piece of gauze to his forehead - however the gauze already has some "blood" on it - a feature the camera obviously wasn't supposed to catch. When Jeanie comes over to check it out, he pulls the gauze away from himself and - voila - there's the bloodstain.
Revealing mistake: When Nova blasts through the building, the wall where the hole is created has already been drawn as misshapen and discolored, likely to make it easier for the animators to animate. (00:02:53)
Revealing mistake: When Ellen and the rest are on the ski lift, it becomes apparent that they are being filmed in front of a green screen because as the lift chair in front of them sways back and forth it disappears into it on the left side. (00:02:05)
Rejoice! I Am Ultimo Thy Deliverer - S1-E2
Revealing mistake: When Mandarin and Modok are flying towards Ultimo in order to regain control over it, there is a noticeable jump cut, as evidenced by the clouds in the sky suddenly changing.
Life Lessons - S1-E4
Revealing mistake: When Danziger and True are pursuing Gaal, they drive up next to Gaal and his horse. In several shots it's obvious it isn't Danziger driving, but a stunt double. (00:47:10)