Revealing mistakes: After Nick gets off of the merry-go-round, there is a close-up of Asta also exiting the merry-go round. If you look at Asta's front paws you can see the straps and fishing line used to pull his legs out from under him. This was done to make him lose his balance and give him the appearance of being dizzy from riding around in circles.
Continuity: When Nick Jr. is trying to get Nick to drink milk, Jr., is alternately holding/not holding his glass between shots.
Crew or equipment visible: When Nick returns to the locker room at the race track, and Asta is scared off by the black kitten, Nick passes an office. You can see a man in the reflection of the window. He is wearing a white shirt and appears to be giving hand commands to Asta. His movements mimic Nick's at first, but when Nick turns to head for the shower room, the man in the white shirt stays in the same position.
Continuity: Prior to Nick going into "Whitey" Barrow's apartment, when the police have already searched it, the camera cuts to Asta with the leash on the floor. Next shot is Nick opening the door with the leash in his hand.
Errors in geography: Bringing back Sam Levine as Lt. Abrams of the San Francisco PD from AFTER THE THIN MAN is a welcome addition to the cast. However, a San Francisco homicide detective wouldn't have had jurisdiction at the racetrack. The only possible area horse racetrack would have been Berkeley's Golden Gate Fields (opened 1941), which is well outside the San Francisco city limits and is reached by driving across the San Francisco Oakland Bay Bridge (where Nick got his speeding ticket and police escort to the track).
Continuity: When Nick and Nora go to the restaurant and order the Sea Bass, Asta breaks away and runs through the crowd and causes a brawl. When he starts running towards the revolving door, he has a leash attached. When he enters the revolving door, the leash is gone.
Continuity: When Nick is pulled over by the motorcycle cop for speeding, the window on Nora's side of the car changes from being up when as the car slows down, to completely down when it stops.
Continuity: When Nick visits the apartment of Clair Porter, they're seated at a small table, with a centerpiece of flowers floating in water. Nick is smoking a cigarette. The cigarette has burned down to a very short length. Then, as he gets up, the cigarette is seen to be almost a full length cigarette.