Continuity: When the Canadian motorcycle police drive up and speak to the boat keeper about George Loomis they're all in direct sunlight with no trees anywhere near them. When they leave several shots later it must be an entirely different time of day because shade from the trees across the street covers the entire set.

Continuity: Mr. Qua and the Cutlers walk away from the Loomis' room after talking to Marilyn. If you look closely the stonewall to the left of them is not in direct sunlight as it was a few shots earlier when they walked up to the door.

Continuity: When the Canadian motorcycle police drive up and speak to the boat keeper about George Loomis one is wearing a white shirt and the other a blue shirt. In the next close-up shot their both wearing blue shirts.

Continuity: George Loomis goes over the falls and Polly is safely on an island in the middle of the river with green trees on it. Several shots later the trees are purple.

Continuity: George Loomis tries to steal the boat and pulls the ignition wires straight out from under the lock. No one touches them but the next time we see them they're hanging differently.

Visible crew/equipment: George Loomis talks to Polly in the boat and looking outside the window it's easy to see that there's no island in front of them. A few shots later it's obvious that the island is superimposed on the falls.

Continuity: Inspector Starkey gets into the police car before Ray Cutler, who sits in the rear driver side seat as they pull away. Several shots later we see them again in a close-up chasing George Loomis and their positions in the rear of the police car have reversed.

Continuity: George Loomis throws a lit cigarette at the ash tray on the table to the right of the door as Polly Cutler knocks. We see the cigarette smoldering on the table but two shots later after she enters we see the same spot again and it's gone without anyone going near it.

Continuity: Two Canadian motorcycle police drive up and speak to the boat keeper about George Loomis, and a prominent tire mark is on the side of the road in front of the black car. The next time we see this spot as Ray and Mr. Kettering run to the boat it's not there.

Continuity: Ray Cutler decides to leave the Rainbow Cabins and says to Polly, "Give me a hand with this stuff, will ya, Honey". As he says this he picks up a suitcase which has nothing on top of it, but when we saw it earlier in the scene there were clothes on top of it.

Continuity: During the outdoor party at the Rainbow Cabins Marilyn walks out and asks the DJ to play "Kiss". No one goes near them but the three chairs that she passes on her right move about a foot closer to the record player when she walks away.

Continuity: Both Marilyn and Jean's faces are dry as bones in the scene below Niagara Falls but Marilyn's lover is drenched.

Continuity: As George Loomis tries to steal the boat there's an ice bucket underneath the table to the right of the steering wheel. Later Polly comes back with some beer and grabs for the ice bucket, which has been rotated 45 degrees even though no one went near it.

Factual error: Marilyn and the Cutler's follow Inspector Starkey down to the bottom of The Scenic Tunnel Trip to identify George's shoes and when they come up Marilyn hears the song "Kiss" chiming from the bell tower. This is an obvious mistake as the shot of the bell tower that we see here is taken from the American side of the falls and The Scenic Tunnel Trip is on the Canadian side of the falls.

Continuity: Polly Cutler enters cabin B in order to put some Mercurochrome on George Loomis' cut and the do not disturb sign on the door knob is tilted to the left. No one goes near it but later in the scene it's been set straight.

Continuity: At the bottom of the Scenic Tunnel Tour, Polly runs into Marilyn kissing her lover. At first the gentleman has his hands around her waist. Then in the next shot his right hand is holding her face.

Continuity: At night the Rainbow Cabins has a little outdoor party. The Cutlers are dancing together, and when the song stops Ray has his arms around Polly's shoulders. In the next shot his arms are around her waist.

Continuity: As Polly and George Loomis are rushing down the middle of the Niagara River a tree appears above Polly's head on the back of the boat.

Continuity: George Loomis strangles Marilyn who falls to the floor of in the bell tower holding a yellow scarf near her face. In the next shot it's held away from her body.

Continuity: Before George Loomis strangles Marilyn in the bell tower she knocks everything out of her pocketbook looking for a dime to make a call on the second floor pay phone. We see the items on the floor as George walks past on his way to kill her, but later when he returns and picks up her lipstick everything has been moved.