After two birds break the glass on the phone booth, it appears that the glass isn't shattered when Melanie is grabbed out of it.
When Melanie is approaching Mitch's house in the boat, and even while she's walking down his dock after leaving the love birds, his car is parked pointing directly out of the garage. But after she paddles away and he walks from the barn to the house, and for the remainder of the scene, the car is parked at an angle to the garage.
When the gas station attendant is hit by a gull, he falls face down, and his body is angled toward the camera. Mitch and some other men go to help him, and in the last shot of them together, he is face up and his body is angled to the left. There is quick cutting in this sequence, and not enough time between shots for the men to have moved the attendant.
Annie and Melanie open the door to Annie's house when a seagull hits it. As the door opens houses are clearly visible across the road, after they look up again from the dead bird the view is now the bay with no houses at all.
During the bird attack on the house, Melanie falls back, almost swooning and crushes a lamp-shade. But, during the rest of the movie, the lampshade remains in perfect condition.
When Melanie gets out of the boat after the seagull attack she appears not to have her purse on the pan-and-scan version.
Even though later in the film it is shown that the birds can make their way into buildings, the bird-attack scene at the schoolhouse makes no sense. Having the children run all the way down the road during the bird attack was far more dangerous than staying in the school, or if they wanted to seek shelter in a building without such large windows they could have run the much shorter distance to Annie's house just beyond the school.
When Mitch is boarding up the house, he does not even use nails for the last one. All he does is set the board on top of the bottom one and tap it with the hammer.
When Melanie and Mitch are together on top of the bluff at the children's party, each person casts two sets of shadows.
When Melanie is climbing upstairs we see her shadow on the wall, even though the only light source is the flashlight she is using.
When the gull breaks through Mitch's window toward the end hands can be seen thrusting the bird toward Mitch.
When Melanie is driving up the coast road, a shot shows the lovebirds sitting in their cage on the floor. The floor of the car shown looks nothing like what the floor of an Aston Martin from this era would look like.
Melanie's put on the settee and when she comes round she starts flailing her arms around as if trying to protect herself from the birds. Shadows of her arms are cast over the settee and her head but the only light is coming from the fire and Mitch is sat on the edge of the settee between it and her.
Even though the film is set in Northern California several of the characters speak with New England accents.
Inside Mitch's house, after the windows are boarded up an unlit wall lamp has it's shadow cast on an adjoining wall despite the only lamp lit is suspended from the ceiling in the middle of the room.
Melanie goes up stairs to investigate a noise and is trapped in a bedroom and attacked by birds which have broken in through the roof. Mitch and his mother rescue her but with the electricity cut off they're reliant on oil lamps for illumination. As Mitch starts to carry Melanie down stairs his mother picks up the lamp holding it in front of her but her strong shadow cast against the wall is obviously from a film lamp behind her.
When Melanie enters Bodega bay school for first time, we can hear the child singing even when they turn around to see Melanie, and are clearly not moving their lips.
Invited to the Brenners' for dinner, Melanie plays the piano while Cathy talks to her. But Melanie's fingers don't match the melody, especially the right hand's higher notes.
While Melanie is driving to Bodega Bay with the love birds, she is seen driving very fast and screeching around every corner, yet the road is gravel until she arrives within the town limits.
When Melanie is driving up the coast road, a shot shows the lovebirds sitting in their cage on the floor. Audio clearly has a gear shift sound, but the shadow of the gear shift never moves, nor is a shadow hand shown.
After Melanie delivers the lovebirds to the Brenner home, the camera follows her as she walks back along the jetty to her boat, with the dolly track clearly visible.
When Melanie is trapped upstairs flailing at the attacking birds with the "flashlight" the power cord is briefly visible entering her sleeve. Note also the typical floodlight patterned glass on the end; sometimes an actual flashlight of that era couldn't put out enough light for the needed effect. These movie flashlights can often be recognized by the oversized bell - like reflector housing as in the "Sound of Music".
In the opening scene in San Francisco, when Melanie Daniels crosses the street at Union Square, off to the right a location assistant in a white coat can be seen asking two women to refrain from also crossing the street at that time so as not to mess up Tippi Hedren's shot.
When the fire starts at the gas station and an overhead view is shown, you can see water spraying onto the fire from 2 directions. This, in spite of the fact that the fire has just begun and you cannot see fire engines. A few moments later, you can hear sirens as fire trucks arrive on scene.
When Melanie was driving her car to deliver the lovebirds, there's a shot of the front of the car and the camera is reflected in the window.
When Melanie crosses the bay to Mitch's house in the dinghy his dock is directly across from the town. But from atop the hillside beside his house the town is nowhere to be seen.
Melanie asks for Mitch's sister's name to write it on a card, but when she is told "Cathy", she doesn't ask how to spell it, even though there are at least four ways to spell it (Cathy, Cathie, Kathy, and Kathie).