When Wayne is fighting on the dock, he threatens Keller with his unsheathed knife. When he turns back to the others, the knife is no longer in his hand, though he's had no opportunity to sheath it.
The film begins with Jessica Fletcher and Wayne Metzger/Stearns traveling by air from New York to Cabot Cove. A Boeing 737 is shown flying, but this is one of Boeing's prototypes from the 1960's, in Boeing livery, rather than an airline plane. The next scene shows the aircraft interior, but this clearly is a much smaller aircraft than a 737, and in a VIP configuration.
When Jessica and Seth are shopping for a lobster for dinner, the fish monger wraps the lobster in newspaper and bags it. However, when lobster is still alive, it's packed in a watertight container until time for it to be dropped into the water for cooking.
At the end of the show, when Wayne is in the hospital, the IV in his hand is placed in the wrong direction.