In the episode where Joey and Ben are trying out for the same soup commercial, Carol asks Joey to watch Ben while she goes to the bathroom. When Joey is talking to Ben about stardom and being famous, the camera goes back and forth between Joey and Ben. If you watch Ben's big stack of Legos, the colors of the stack obviously changes. It goes from lots of yellow, to no yellow at all, then a couple Legos that are yellow. I've seen this episode more than once so I'm sure it's a slip up.