When Dr. Carey drives erratically to intimidate his passenger into telling him what she knows about the murder, her passenger side window alternates between completely open and completely closed.
When Carey jumps the bridge, the front hubcaps can be seen flying off the front wheels of his station wagon. The hubcaps then reappear back on the car.
When Carey jumps the bridge and drives through gate, the front headlights can be seen breaking and the there are several dents in the car. When Carey drops off Karen the car looks fine.
When Dr. Carey goes to see J. D. Randall, in the shot from behind Randall, there is nothing on his desk blotter. But, in the shot from Carey's point of view, there is a piece of paper there.
The girl, Karen, dies after driving herself home from the botched abortion. At the jail, when Captain Pearson meets Carey, he says to him, "Not a $10 doxy. A 15 year year old girl from a good family." Surely, being a captain of police, he knows the legal driving age in Massachusetts has always been 16.
During the autopsy, the cadaver is clearly breathing.
A photographer takes a picture of Carey in bed with Georgia. But he is outside of Carey's bedroom and takes the photo through the window with a flash. As the Carey's bedroom was dark, the flash would have turned the glass window panes into a mirror and resulted in an image of the photographer himself as he shot the picture or (at the very least) a photo of the photographer over the image of Carey and Georgia in bed. The image would NOT have been the clear (studio quality) photo that Carey had blown up and printed (which he gave to Randall).
When Carey is taking Lydia for a wild ride in his station wagon, as he turns onto the road with the drawbridge, there is a marker for California state route 160 at the intersection - although they are supposed to be in Massachusetts.
When Dr. Carey calls Capt. Pearson from a phone booth, he only dials five numbers, not seven.