After getting a visit from the vampirized Danny Glick, Mark is backing away from his bedroom window with a cross held in his outstretched hand. He then pulls the cross to his chest. In the next shot, his arm is still stretched out in front of him.
The blood drop on Mike Ryerson's pyjama top changes. When first seen (when he is newly dead) it is a large spot on the pocket. Later, when he visits the doctor, the spot is nearly invisible in some shots. In other shots it is a very small drop slightly above the pocket.
In the Marsten House, Straker picks Bill up with his hands on Bill's arms, just below the shoulders. But as he approaches the antlers, Straker has one hand on Bill's arm and one hand clutching his tie.
As Ben and Dr. Norton drive around town preparing to go to the Marsten House, the sun shifts several times between being low and being high.
Ned Tebbits is waiting for Ben Mears in his room at Eva's boarding house. How did he gain entrance to Ben's room without Eva knowing? It is possible Eva wasn't home at the time Ned got into the house, or simply didn't hear him come in (and being a boarding house, in a small town in the 1970s, the front door would most likely be unlocked throughout the day).
In the meeting with Mark, his parents, and Father Callahan, Barlow (the vampire) simply breaks into the house without any invitation by its occupants. All of the other vampires in the movie need to be invited in. However, Barlow is a powerful master vampire for whom such "rules" may not apply. Note how he doesn't recoil from Father Callahan's cross. In fact, he actually touches it and throws it to the floor.
Just before the window in the Petrie's kitchen blows inward, a very visible wire can be seen pulling the frame of the window inwards.
After Danny Glick visits Mark outside Mark's bedroom window, Mark shows Danny the cross he took off the model on his desk and tells Danny to "Go away!". As the vampirized Danny begins to "float" backwards away from the closed window, you can see Danny is sitting in a chair on a boom that is lifting him away.
When Mark goes to the Marsten house to kill Barlow, he pulls out two lock picks from a small case in order to break in. Then he clearly inserts the handle of one pick into the padlock, rather than the toothed end.
When Barlow is in Mark's kitchen, the make-up line on Barlow's neck is visible.