Revealing mistake: During the opening sequence of the second season of Soap, the families are having their picture taken when the roof collapses on them. Billy Crystal closes his eyes and keeps them closed before the roof falls, showing he knew what was about to happen.
Episode 70 - S4-E1
Revealing mistake: Toward the end of the episode, Bert receives an envelope with pictures of him and Danny at a motel with some women. As they look at photos, Bert hands Danny some photos. Danny crosses left. Bert turns stack of photos over and says there is a note. He reads note and turns photos back over afterwards. The backs of the photos are blank. Danny crosses right to Bert holding photos. You can see on the back of Danny's photos the note Bert just read from the other side of the room.