At the end of the movie when Mitch gets in Melanie's car to take it out from the garage, he closes the window of the car. After a minute when he gets of the car in front of the garage the window is open.
When Malanie 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.
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.
The kitchen window in the Brenner's house is facing the wrong way. Based on the dining room orientation, the sink and window of the kitchen should be on the right, facing the rear of the house, when one walks in from the dining room. Instead, it is to the left, which would face a solid wall with no place for a window.
When Melanie Daniels is sneaking up Mitch's dock to deliver the lovebirds, she looks over at the barn he's in, the sky has a complete gray cloud cover. Seconds later, she looks at the barn, not a cloud in the blue sky.
When Melanie arrives at the Brenners' dock, it is high tide and she easily climbs out of her boat to their dock, which are nearly level to each other. The same is true when she returns to her boat after leaving the lovebirds. However, when Mitch comes out with his binoculars right after seeing Melanie's boat, the tide has gone out quite far. The waterline has dropped considerably and a small boat near the dock can be seen floating several feet below it. Melanie would not have been able to easily climb in and out of her outboard under these conditions. The tide, while going out dramatically in a shallow bay like this one, cannot possibly go down that quickly in real time. Obviously, a lot more time has gone by between Melanie's return to her outboard and Mitch's appearance with his binoculars, even though the action is supposed to take place only minutes apart.
When Melanie pulls her car into the Brenner's yard for dinner, it is facing away from the house, which is on her right. When Mitch walks her to her car after dinner, the car has turned around 180 degrees, and the house is now on the left of the car.
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.
When Melanie arrives for dinner with Mitch and his family, the driver's seat of her car is clearly set further back than the rest of the front seats. When she leaves, she gets into the car and we see the driver's seat is now perfectly aligned with the rest of the seats.
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.
When Melanie pulls up to the Brenner's dock and leaves again after dropping off the lovebirds, there is no other boat visible at the dock. However, when Mitch comes out with his binoculars, a shot of the dock reveals a small boat tied to it. That boat was not there when Melanie arrived at the dock only minutes before.
Melanie is able to deliver the lovebirds by piloting a boat to the Brenner's dock. At Cathy's party the next day, we see from the top of the hill that the dock is not accessible by water (water level too low).
The difference between high and low tide is quite dramatic in Bodega Bay. The dock would not be accessible during low tide.
When Lydia sees Dan Fawcett's kitchen, the cups are nicely hanging from a shelf, but obviously broken by the intruding birds. Unless somebody arranged this afterwards, most of the cups would be shattered on the floor.
While in the car when the crows attack the school, Melanie's left hand is by her head when she beeps the horn. In the next shot, her hand is on the steering wheel while beeping the horn, the next shot her hand is by her head again.
At Cathy's birthday party, when Mitchell and Danielle climb the small hillock to chat, Mitchell is holding a bottle of colored liquid, probably whiskey. After the camera angle changes, when they approach the top, same bottle now has some clear liquid.
When Melanie is in the boat and attacked by the gull, she is wearing a gold necklace. When she's looking out the window in the diner, the necklace is gone. The necklace is also not visible in the phone booth. I would have to watch the movie again to see if she arrives to the diner with her mink jacket and scarf or maybe she left both of them in the car before entering the diner.
When Lydia drives off in the pickup truck from the Brenner place to visit a neighbor she drives away in bright sunlight with a clear sky. A moment later she arrives at her neighbors farm and the sky is completely overcast.
When the actors enter the Brenner house there is a fireplace to their left in the studio set. But the exterior shots of the house-front show no fireplace at all, and aerial shots show only one chimney at the far end of the building towards the barn.
While chatting, Annie leans against Melanie's car after they have just met. Melanie thanks Annie and speeds off. In the next shot and while Melanie has clearly left, Annie seems to just having left her prop and stands on her feet again. Also the car sound can be heard in a distance.
When Melanie is calling her father from the restaurant, her left hand is holding the phone wire. In the next shot, her hand is still holding the phone wire but she has a much looser grip on it and her hand is closer to the phone.
When the gull attacks Melanie, at the 24th minute, we see Mitch jumping from the pontoon twice: once from Melanie's point of view, then a second time from the pontoon. And Mitch's attitude is clearly not the same in the two shots.
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 goes upstairs with the flashlight, there's a close shot of the brass doorknob as she arrives there. Two reflections of light sources are visible on the knob, when there should be only one from the flashlight.
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".
Mrs. Bundy says she recalls a "large flock of seagulls" lost in fog and headed toward Santa Cruz. As an amateur ornithologist, she should have known that a group of seagulls are referred to as colonies.
We see Mitch's car in the film and he has obviously driven it to Bodega Bay, but at the end of the movie, only the family truck and Melanie's car are seen, and the family uses Melanie's little sports car to leave when Mitch's car would have been more comfortable. Where did Mitch's car go? It seems to have disappeared with no explanation.
During the scene where the red haired girl falls, she breaks her glasses, however her face was too close to the ground for the glasses to shatter so badly. The cracks on both lenses are also thick white star burst patterns showing they had been already smashed by something like a hammer, and even if the glasses had genuinely smashed from landing on the ground, the damage would not be identical to both lenses seeing as how they landed at an angle, only one lens would have sustained the most damage and left one side still in tact. The glasses were broken before they were even dropped.
After Melanie is attacked upstairs, the "blood" on her face is obviously just painted on, with no evidence of actual scratches. It's especially noticeable when the "blood" is being wiped off in a closeup.