Continuity mistake: At the Rainbow Cabins, Polly Cutler speaks to the Kettering's and holds a bouquet throughout the scene, and it keeps changing positions between shots. (00:45:05)
Continuity mistake: Polly decides to take a nap in cabin B and the ash tray on the night table moves to the edge during the scene without her going near it. (00:46:45)
Continuity mistake: Marilyn speaks to the cabin manager and says, "It's the first good sleep he's had in over a week" and the fur on her collar is motionless. In the next shot the wind is blowing it continuously. (00:08:30)
Continuity mistake: Marilyn's shadow falls on the door as she speaks to Mr. Qua and the Cutlers, and after finishing she goes back into her room. In the next shot the lighting has changed and Mr. Qua's shadow falls in the opposite direction onto the Cutlers as he speaks to them. (00:09:30)
Continuity mistake: Mr. Qua is watering the flowers and as Polly Cutler speaks to the Kettering's we see the front of the car and there's no water on the gravel by the tire. After they get into the car and drive away in the next shot, there's a lot of water on the gravel. (00:45:15)
Other mistake: The first time we see George Loomis back at the Rainbow Cabins after his supposed death he's by the garbage cans in the back of cabin B with a brick wall on the left. The next time we see him two shots later the film has been reversed with the brick wall now being on the right. (00:46:45)
Continuity mistake: After fishing on the Niagara river with the Cutler's, Mr. Kettering pulls his boat up to a dock that is in the shade. In the next shot the dock is in the sunlight. (01:11:30)
Other mistake: The Cutler's now occupy cabin B at the Rainbow Cabins and just before we see George Loomis by the garbage cans in the back of the cabin Polly decides to take a nap. When she gets up from the bed to close the Venetian blinds we see the pillow case and it's white, but two shots later after the blinds are closed she lays down again and the pillow case has a huge dark make up stain on it from several previous takes. (00:46:20)
Continuity mistake: Marilyn's lover writes a one line message to her on a postcard and places it back into the postcard rack. She walks over and reads it and we now see that there are 6 lines written on the back of the card. (00:34:05)
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)
Continuity mistake: After George Loomis shuts the lights Polly Cutler looks to the left at the falls in the dark, through the back window. This is the wrong direction as we see later in the movie as Marilyn has to look to the right to see the falls during the day. (00:23:15 - 00:36:15)
Other mistake: In Canada the Cutlers take the Scenic Tunnel tour, and if you look closely the cash register keeps ringing up zero as they and the people in front of them purchase tickets. (00:12:20)
Continuity mistake: As the Cutlers drive into the Rainbow Cabins it's clear to see that Polly's vent window is closed. She doesn't touch it but when the manager helps her out of the car it's open. (00:07:10)
Continuity mistake: The Cutlers drive up to the Rainbow Cabins and Ray reaches for the ignition to turn the car off as they speak to the manager. In the next shot his right hand is leaning on the front car seat. (00:06:30)
Continuity mistake: The manager knocks on the door to cabin B and the stone post in the background on the left of the screen is in direct sunlight. Two minutes of uninterrupted movie time goes by but as the Cutlers get ready to leave the stone post, and the falls behind them are no longer in direct sunlight. (00:08:00)
Visible crew/equipment: At the Rainbow Cabins the Cutlers sit in their car and the manager says, "I've got you down for cabin B". The shadow of a boom mike moves across his face as he approaches the car. (00:06:40)
Visible crew/equipment: The Cutlers drive over the bridge into Canada and speak with the customs officer. If you look closely when the camera films over the customs officers back you can see the reflection of the crew standing behind him in the windows behind the car. (00:05:40)
Continuity mistake: Ray Cutler says to the customs officer, "I'm going to catch up on my reading" and his right arm is leaning on the seat of the car. In the next shot his arm is at his side. (00:05:45)
Continuity mistake: Marilyn walks up to the ticket booth and gets a refund for one of the tickets to Chicago that she bought earlier in the movie. Looking at her luggage we see no marks on it at all. She picks it up the same way she puts it down, but in the next shot a large black mark appears on the front of it. (01:01:15)
Continuity mistake: As Polly Cutler lays out on a beach chair sunning herself Ray steps back and decides to take a picture of her sitting there. Niagara Falls, which are always seen behind them are not in this shot, which has obviously been filmed on a sound stage. The bushes against the stone pillar are also different. (00:34:55)
