The bonded messenger company's gray sedan is clearly shown bearing license plate MPF686, and Chief Dan Mathews takes a phone call, after which he describes said plate as "Mary, Paul, Frank, 6, 8, 6". However, later in the story, Ralph Wilson tells Mathews that Henry Wigram's personal red convertible has the same license plate number: MPF686. Still later in the story, said red convertible is clearly shown bearing a different plate numbered MPF669.
When John Grolier pulls his station wagon up to the Maple Leaf Motel, the previously shown front license plate has disappeared. In the next shot where he exits from the car, it has reappeared.
When Dan Matthews is outside the Wigram house and Grolier is inside. Grolier shoots through the door but no bullet holes are on outside of the door. When Matthews opens front door, there are two "bullet holes" inside, pretty good trick to have a bulletproof door.
As Dan Matthews is checking the dead body of Alma Wigram in the Maple Leaf Motel cabin where she was killed by John Grolier a mans hat is clearly visible laying on the bed in the background. It is obviously Grolier's hat as he was the only occupant of the cabin. Groiler has already left the cabin and is on his way to the Wigram residence to try and find the stolen money. Despite the fact that his hat was left on the bed in the cabin he is wearing it when he gets to the house.
When Grolier walks outside of his room, and goes to the motel phone booth to make a phone call (presumably to call Mrs Wigrahm) a boom microphone is clearly reflected in the glass picture above his head.
When Dan exits the motel office after talking to the clerk, you can see someone crouching down in the bushes behind him. Looks like they may be wearing a highway patrol cap. UPDATE: Looking closely, it is not a "someone" but it is a beagle-type dog in a cage.
The part of Alma Wigram is credited to Jean Ruth when it was actually Jean R. Maxey who was also in 'Deaf Mute'.