While Marvin Claridge is being cross-examined by Perry Mason, there is also a cutaway shot showing Claridge sitting in court next to his daughter and behind Hamilton Burger.
Early in the show, when Everett Dorrell tried to turn his headlights on, he pulled the headlight switch out by one pull detent. All Ford products of that time, including Dorrell's 1960 Mercury, used a three-point headlamp switch (for that matter, so did GM, AMC, Studebaker and Chrysler Corp. products), so pulling the switch out by one detent would activate only the parking lights. Another detent pull would be necessary to activate the headlights.
When Perry goes to visit Alexander Hill at his apartment, a second shadow (NOT Perry's) appears on Hill's door just before it is opened.
When the fire chief arrives to put the fire out at Richard Hammond's garage, he looks down for his mark before he speaks.
When Helen Austin is struck by Everett Dorrell's car (an obvious dummy was used), the wipers are not in use, and tucked below the windshield (as seen from inside the car). After Everett Dorrell stops the car and gets out, the wipers are stopped in the middle of the windshield.
When Everett Dorell is about to drive down his driveway, a camera shot of the headlight area of the car shows a person's reflection in the chrome trim.
In the final courtroom scene, Perry accuses the killer of murdering Helen Austin after he followed her and knew whom she was blackmailing, and he no longer needed Helen. Then in the final explanation, Perry states that the killer had been getting half of Helen's blackmail because he threatened to go to the blackmail victim's wife. Therefore, the killer knew who the victim was before the murder, and Perry's accusation in court as to why Helen was killed doesn't add up.
The murderer calls a third party and entices him to leave home, then throws the body of the murder victim in front of the third party's car. Given the semi-rural setting of the third party's home, it seems impossible that the murderer could have found a public phone booth close enough to make the call and still hurry back in time.