At the beginning, when Arthur Hamilton is on the train, he gets his newspaper and starts doing crosswords with a pen in his right hand. Later on he signs the contract at the clinic with his holding the pen in his left hand.
During the grape crushing scene, Tony Wilson's girlfriend, Nora, starts to strip-off. Her dress is unzipped down the back. The next shot it is clearly zipped to the top and then unzipped again in the next shot.
When Tony is being shown the blackmail film that is calculated to get him to cooperate, the blackmailer sits in the guest chair next to Tony. After an assistance enters the room, the blackmailer rises to greet him, then returns to the chair to find Tony's hat has mysteriously appeared on the chair, and has to be removed for him to sit down again.
The goof item below may give away important plot points.
Aside from the fact that it would have robbed actor Rock Hudson of his big berserk scene and cleared up some fuzzy plot points that wouldn't otherwise have been evident, why didn't The Company routinely sedate Wilson (and other failed "reborns") before wheeling him into the operating room to murder him rather than to have some hospital staffers simply warn him to calm down and insert a gag in his mouth while explaining they were about to commit euthanasia on him? Obviously, anyone strapped onto a gurney under the impression they're en route to a plastic surgery procedure is going to raise hell when they learn they're actually about to be murdered - something this outfit should have been well aware of long ago.