Trivia: Unusually enough for a television show devoted to a homicide detective and the way he unravels the plans of cunning murderers, the fact is that Columbo has nothing to do in this episode. Doctor Collier is seriously assaulted by Carl Donner who then goes on to violently attack his wife. Use of deadly force to prevent such an attack is allowed in the United States. Collier does not commit murder; he doesn't even commit a crime. You'd think such a hightly educated man would know enough to keep his head, call the police and explain what had happened. He wouldn't even be charged.
Trivia: A clever, subtle hint as to Mason's guilt - Columbo arrives at the animal pound just in time to stop him feeding Laurel and Hardy (the dogs he trained to kill on command) a large amount of chocolate treats. He has planned this murder meticulously, and he would be aware that chocolate is extremely toxic to dogs. The amount he is planning to feed them from the bulging bag of large chocolate balls he is holding would kill both dogs within hours if ingested.