Revealing mistake: As Marilyn walks out during the outdoor party at the Rainbow Cabins, we see an artificial painted backdrop of Niagara Falls behind her that is nowhere near the actual falls that we saw earlier in the movie. (00:17:20)
Revealing mistake: During the outdoor party at the Rainbow Cabins Marilyn asks the DJ to play "Kiss" in order to drive her husband George nuts, and after a couple of minutes he comes out and smashes the record. As he walks back to cabin B it's obvious this is a set as there's nothing inside the room except a blank wall. (00:20:15)