Continuity mistake: Magnum shoots at the bad guys who flee after setting on fire the stable of the rival. In close-up, Tom Selleck acts a bit, with an expression of disappointment at missing them and some energetic gesture. None of which happens in the longshot, where he repeats the same action but with no such flair. (00:23:00)
Continuity mistake: Higgins and Magnum bicker quite a bit about Robin Masters' box, the horse client and rugged chukkers. During the whole scene, the same extras walk back and forth repeatedly with no logic. For instance, the woman in blue shirt and a straw hat, popping up behind Higgins first and then behind Magnum in the opposite direction when Higgins asks "Another uncle?" (00:25:30)
Continuity mistake: Magnum before the race tells Adelaide to "Ride like the champion you are." Behind her, a woman with a beige hat with a leather band walks by, along a man with curly blonde hair. Same two pass her by, again from the same direction, in the next shot several seconds later, and again another few seconds later when he tells her to smile. (00:27:15)
Continuity mistake: Rick and TC their back to Magnum and scoff at him. Magnum chases his primadonna friends to convince them to help him. During this scene, the same rider approaches the gate, accompanied by a stable worker with a baseball cap that is first red, then yellow. (00:29:10)
Continuity mistake: Inside Higgins' study you can get a great look at Magnum's dirty shoes when he sits with his feet up on the desk. Those shoes have a blue logo on the tongue. Later there's a close-up of Magnum and Adelaide's feet when Magnum drops the gun in the stable, and the shoes are very similar but different, lacking the blue logo. (00:39:15 - 00:44:15)
Character mistake: The day of the race, Higgins reacts to Adelaide mentioning Norman as if it were the first time he ever heard the name, but he was present when she mentioned him, and the case. Not being all that involved, technically he didn't have to remember that, but he remembered the detail of the uncle, and forgetting that the woman was talking about someone being murdered, is quite odd - and is just done for the cheap gag that follows.
Continuity mistake: When Agatha Kimball tells Amy at the piano "No, I was talking about your cologne", Andrea Marcovicci's hands both jump on the cup at the cut. She was holding it with just one hand. (00:05:00)
Continuity mistake: Mrs. Kimball's wheelchair and Mrs. Kimball herself are in position and angles different in each shot during the scene of the fall; the chair faces right, left, right, and the old lady is suddenly perfectly on the ramp at the end after falling prone. (00:05:40)
Revealing mistake: When Agatha Kimball gets her wheelchair caught in a gap between the step and the ramp, stagehands can be seen as they safely hold Mercedes McCambridge to avoid her getting hurt. (00:05:45)
Revealing mistake: Mrs. Kimball falls off the wheelchair in an alternative take, featuring a stuntperson instead of the elder actress. Problem is, the stuntperson is barefoot, and Mercedes McCambridge wears socks and slippers. (00:05:50)
Continuity mistake: Magnum is going to deliver the blackmail money. As he gets out of the car in the aerial longshot, he has dark shoes, as opposed to the white trainers he sports during the episode. (00:13:20)
Other mistake: Magnum runs away to chase the sniper. A few extras promptly start yelling and screaming despite the fact that from their position they can't have properly seen the victim of the sniper yet (and there's no blood). (00:14:50)
Visible crew/equipment: Magnum lost the car he was chasing. He comes across a police car and stops at the crossroads to avoid getting stuck giving too many explanations. The road is outside of town and kinda in the middle of nowhere, but in the side mirror there's a bunch of people watching the scene. (00:16:20)
Continuity mistake: Inside Frank La Rue's apartment, Magnum approaches his suitcase. The position of the suitcase in the POV shot does not match at all the following view. (00:19:40)
Revealing mistake: After Magnum gets punched by Ted Danson, he drives off. Oddly enough, he drives by TC's van, parked in front of one of the villas of the area, and that has no business being there. (00:24:05)
Continuity mistake: When TC says "This ain't no lunch", his right hand jumps on the table, when it was off it when he dropped the burger in its box. (00:25:15)
