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)
Continuity mistake: Polly Cutler enters cabin B in order to put some Mercurochrome on George Loomis' cut hand. At first the yellow notice on the left door post is entirely in the light, then in the next shot as she walks through the door the lighting has changed and it's in the shade. (00:20:45)
Continuity mistake: As George Loomis goes over to the front door and shuts the lights so that Polly Cutler can see the falls in the dark, a pink sweater appears on the red and white chair behind him. (00:23:00)
Continuity mistake: After Polly Cutler enters cabin B in order to put some Mercurochrome on George Loomis' cut hand the model car that he has been assembling sits on the table to the right of the front door. It moves closer to the ashtray as the scene progresses. (00:22:55)
Continuity mistake: Mr. Qua and the rocking chair that he's sitting in as the Cutlers pull up, are in the shade. Now a few minutes later, Marilyn walks past Polly as she leaves the cabins, and the rocking chair is in direct sunlight. (00:10:05)
Continuity mistake: As the Cutlers set sail on the "Maid of The Mist" it's mid-day. Two shots later we see the boat in a long shot and it's late afternoon. (00:11:45)
Continuity mistake: Marilyn walks past the office as she leaves the cabins, and the blinds on the window are down. No one was in the office, but several shots earlier, as the Cutlers drove in, the blinds were up. (00:10:10)
Continuity mistake: When the Cutlers drove into the Rainbow Cabins, the manager threw the newspaper he was reading onto his rocking chair. No one goes near it but when we see the chair again, as he speaks to Marilyn, the newspaper is not there. (00:09:05)
Continuity mistake: After the Cutlers leave the customs officer, Polly says to Ray, "Delayed or not" and the bottom half of her face has a shadow falling across it. In the next shot it's gone. (00:06:05)
Deliberate mistake: Jean Peters' face is dry on the Maid of the Mist boat ride. (00:12:00)
Continuity mistake: Sunlight is coming into this room from all directions. At first it is coming from the right of the screen. Then when Denis O'Dea goes into the kitchen (screen left), sunlight is coming from the other direction. (00:48:40)
Continuity mistake: Marilyn sleeps in her hospital bed as the song "Kiss" plays from the bell tower. At first she's sleeping on her back then in the next shot she's on her side. (00:57:15)
Continuity mistake: George Loomis chases Polly at the Cave Of The Winds and she almost gets killed braking apart the wooden rail as she runs into it. The part of the railing hanging on the left changes position between shots. (00:54:40)
Continuity mistake: At the Rainbow Cabins, Mrs. Kettering hands Polly Cutler a bouquet of roses and the pink bow is on the left. In the next shot the bow is rotated 45 degrees to the right and is now facing Mrs. Kettering. (00:44:10)
Continuity mistake: In bed in their room Marilyn says, "Get me some orange juice Georgie" as she lays in bed on her side. In the next shot she's lying on her back. (00:29:30)
Continuity mistake: At the Rainbow Cabins, Polly Cutler lays out on a beach chair sunning herself as Ray comes out to talk to her. There's a second chair about 10 feet to her right but the in the next shot it moves right up next to her. (00:34:40)
Continuity mistake: Ray Cutler runs out of the cabin office and says to Polly, "How do you like that?". In the overhead shot you can see tire marks on the gravel driveway but in the next shot there are none. (00:34:30)
Continuity mistake: The Cutlers take the Scenic Tunnel Tour and the attendant on the left is handing a gentleman a pair of boots. In the next shot he's standing around getting ready to laugh. (00:12:40)
Visible crew/equipment: After the manager helps Polly out of the car she says, "Cabin B is ours?" and you can see the shadow of the crew moving on the dashboard of the car. (00:07:20)
Continuity mistake: In the first scene of the movie we see Marilyn in bed with a cup and saucer on the edge of the night stand. She doesn't touch it but as George walks in the room the cup moves about six inches back from the edge of the night stand. (00:03:00)
