When Dr. Cahill gets the keys to car #6, a woman is right behind him to get her keys. When he comes out of the vestibule, the woman is already outside ahead of him.
When Dr. Cahill returns car #6, he parks it next to car #5. Later, we see that car #6 is next to car #23. The woman in the red coat gets into #23's passenger seat. Then, moments later, when Dr. Cahill back another car into #6, the car next to it is again marked as #5 and the woman is sitting in it.
At the end of the episode, Columbo gives Cahill a new, wrapped cigar, he opens it and begins to smoke without cutting an airway at the closed end first.
In the "home garage laboratory" there is a shelf of chemical containers marked with their respective formulas. The formulas are written incorrectly.
The body is supposed to have suffered multiple fractures but there is no blood and no wounds.
When MM7 (Robby the Robot) is first seen typing on Dr. Cahill's (José Ferrer) keyboard, there is a clicking sound as it types each key. However, there are two keystrokes that don't have the "click" - the first one from the right side view and the sixth one overall (third from left side/closer up).
The mechanic working on the natural gas powered car mentions "the pilot light keeps going out", but natural gas powered cars are internal combustion engines which use spark plugs and there would be no pilot light.
There are two U.S. Marine Corps officers (Colonel and Lt. Col.) at the war gaming event. Both have hair that is too long (not a regulation cut, today or in 1974). A problem with many TV shows and movies in the past was that extras with regulation military haircuts were not available. The other military service members (U.S. Navy, U.S. Air Force, U.S. Army), although their hair was also long, they were within regulation standards for that time frame.
After searching a lab for a missing pipe, and when Jose Ferrier leaves, Columbo spots broken pieces of a tobacco pipe on a driveway and begins to pick them all up, which is exactly what he should not have done. Evidence found at a crime scene should be carefully handled and bagged for forensic testing, and not just randomly handled, corrupting any forensic tests.
Dr. Cahill smokes his cigar in the computer room. That would have been forbidden. Computers had to be kept in clean rooms.