When Joe is eating the sandwich and talking with Peggy it changes form a bite out of both ends to no bite from both ends as he holds it.
Mannix invites James Conway (Anthony Zerbe) into his office and offers him a cup of coffee. He then hands Conway a cup of coffee while still holding his own cup which Peggy poured for him prior to Conways arrival. Peggy is in the outer office at the time. Unless she had poured Joe two cups of coffee that morning he would not have had a second cup of coffee to offer Mr. Conway.
When Mannix leaves Conway's hideout he notices a sniper in his car's rear view mirror and ducks just before a bullet hits his windshield. This shouldn't have been possible. Those mirrors are aligned so that the driver can see a car on the road behind him. The sniper was on the second story, and the only way Mannix could have seen him would be if the mirror were angled up at a high angle, too high to be of any use in driving.
When the killer calls Mannix in the phone booth, he asks him if he sees a black sedan to his right. The camera shows Mannix's view of the parking lot as he is looking for the black sedan and he looks directly at WHITE car and acknowledges that the BLACK car is there. But there is no black sedan and Mannix goes to a WHITE car, listens to instructions given to him by radio and drives away in the white car.
At one point the killer tries to shoot Mannix from the second floor of the skid row building where James Conway (Anthony Zerbe) has been hiding. Mannix pursues him out onto a fire escape, but near the end of the chase, a poorly-timed closeup of "Mannix" climbing an exterior ladder reveals that it is a stuntman and not Mike Connors.
After a sniper takes a shot at Mannix and puts a bullet through the windshield, Mannix continues to drive with the hole in the windshield. It is clear that it is a squib as there is a black hole on the windshield that you cannot see through.
When Mannix goes to the Welch House to confront the supposed killer he pulls up at night in his car from two seasons ago instead of his car that he presently drives.