When examining the murder scene at the marriage bureau a police officer brings the victim's handbag out to inspector Oxford, who correctly holds it with a handkerchief to keep his fingerprints from contaminating the evidence. He then he sticks his un-gloved hand inside and feels around, thus contaminating it with his own fingerprints.
After the camera goes back down the staircase and out the front door into the market, a man walks past with a big sack of tomatoes to cover the transition from the studio shot to the exterior. Before he passes (the studio shot), the door frame on the right is clean, but afterwards (the exterior), a greasy black stain can be seen on the right of the "real" door frame above the doorbell. Also in the exterior shot, a lampshade and the shadow of the archway over the interior door can be seen reflected in the window over the stairs when no such reflection was seen in the studio shot.
At the start of the movie Blaney is seen finishing the knot on his tie. In the next shot (of him coming down the staircase into the bar), he has the same tie but the colored stripes are different in the knot.
After he orders a triple, Blaney pays the bartender holding the bill in his left hand from bartender's point of view. The camera switches to Blaney's point of view and the same bill is in Blaney's right hand.
As Rusk is leaving Mrs. Blaney's office, he takes another bite of the apple (previously shown as mostly green but ripening into red) and sets it on the desk with the green side facing the camera. At the door, as he turns to see if he's forgotten anything, the closeup shows the apple with the red side facing toward the camera when it should be facing away from it.
(at around 1 min) Richard and Babs arrive at the Coburg Hotel. The exterior shot shows two women with two suitcases standing on right-hand side of the main door outside the hotel, and Babs puts her handbag under her arm. When they enter the hotel, the interior shot shows two couples standing either side of the main entrance outside and suitcases on the pavement on the other side of the main door and Babs is hold her handbag in her right hand.
When Rusk takes Babs to his home, he tells her he lives on the second floor. No British person would say this. From the stairway tracking shot that follows, we see that Rusk lives on the floor above street level, which in Britain is called the first floor.
After the police see the body in the back of the potato truck, they follow it and hit their siren. The truck driver then hits his brakes and the body falls out of the potato truck. This should not happen. The law of inertia means that any unsecured item in the truck will continue to move forward if the truck comes to an abrupt halt (which is the entire reason why we need seat belts in cars - to keep us from flying through the windshield during an accident). The body in the truck *should* have kept moving forward in the bed until it hit the partition separating the bed from the passenger cabin (or more sacks of potatoes).
The (hanging) camera tracks backward, turning 180 degrees as it goes down a staircase, before going out through the front door. As it passes through an internal doorway within Rusk's house, the door frame can be seen sliding back into place after (presumably) sliding out of the way to let the camera pass through it.