After leaving Bedford's Island, Jeff and Carola go to a bar. Jeff sets a drink down in front of Carola, withdraws his hand and goes to sit down. In the next shot, he is withdrawing his hand from her drink and is sitting down again.
When Jeff Caign and Carola Ballister are talking at a lunch counter, you can see in the back projection, the same truck traverse from right to left on five occasions.
The Professor tells a student to start playing scales, and then goes into another room. The sound of the scales stops before the Professor closes the door completely. Then when Jeff and Carola leave the Professor's office, a squeaky note can be heard before they open the door.
Neither Kingby or Jeff check to see if there is a round in the chamber of the gun Carola originally had in her purse.