Continuity mistake: After Melanie signs the card to Cathy she never puts her left glove back on. We're able to see her drive down uninterrupted to the boat and she never puts it on, but when she walks out of the car to the boat it's back on.
Continuity mistake: After Melanie has been bandaged up after her attack, she sits up on the sofa, and you can see two large bloody scratches on her cheek. These scratches disappear when Mitch and Lydia walk Melanie outside to the car.
Continuity mistake: When Tippi Hedren is having her head wound cleaned in the restaurant, Rod Taylor is wiping her blood off with a tissue but it does not actually come off; in the next shot, however, there is clearly no blood on her head.
Continuity mistake: As Lydia carries the birthday cake out, the shades of the window behind her are open. When we see this window again a few seconds later as she runs into the house the shades are closed.
Continuity mistake: Melanie's car changes positions from the time she parks near the front steps of the school. As Melanie walks out of the school to sit by the monkey bars to when she runs back to the school, and then when the children run out of the school.
Continuity mistake: Inside the restaurant Melanie talks to her father on the phone at the bar. The phone's chord changes position between shots. At first it's resting on her sleeve then in the next shot it's on her forearm.
Continuity mistake: After talking to Mitch on the phone, as Melanie sits behind Annie's desk there are two pens on top of the sheets of paper to the left of the pencil holder that were not there before. Neither Annie or Melanie touched a pen or pencil in this scene.