Continuity mistake: When Joan leaves the restaurant, her glass is full. Next time we see it, it's empty.
Revealing mistake: When Cagliostro is stabbed, there's a protruding rectangular pad under his shirt where the knife is stuck.
Revealing mistake: When Jessica rides on the motorcycle, one can see it's a much younger and thinner stunt double who doesn't resemble Angela Lansbury.
Continuity mistake: When Jessica talks to Lt. Bergkamp, she takes her left hand to her ear to improve her hearing, but from the opposite shot, her hand is lowered.
Revealing mistake: After Denton falls off his horse, Jessica arrives and jumps off hers. Her stand-in is a much younger and thinner woman who looks nothing like Angela Lansbury.
Visible crew/equipment: When Jessica is on her horse at the barn, there's a crew member lying on the floor, watching out for Angela Lansbury.
Death Takes a Curtain Call - S1-E9
Visible crew/equipment: When Jessica and the Russians exit the theatre, the whole filming crew and cameras are reflected on the car's fender.
Death Takes a Curtain Call - S1-E9
Continuity mistake: When Jessica questions Eddington, he has his glasses on. An instant shot later, they're on his hand.
Death Takes a Curtain Call - S1-E9
Revealing mistake: When the cops arrive at supper time at Jessica's door, the background is a blatant painted backdrop. (00:31:45)
Death Takes a Curtain Call - S1-E9
Continuity mistake: The way the sheriff hands over the phone to Major Anatole Karzofman differs between the first and second shot, with the handset turning 180ยบ.
Visible crew/equipment: When Jessica gets trapped in the car, lighting equipment is reflected on the window.
Visible crew/equipment: Jessica is at the crime scene with the detective and walks from the back of the set to the cemetery. The moving shadow of the camera is cast on a rocky wall. (00:17:33)
Revealing mistake: When the episode ends and Jessica drives the buggy, she is replaced by a very obvious stunt double with a wig that not only does not resemble her hairstyle, but it's grey as opposed to her light blonde colour.
Visible crew/equipment: After Seth drives Jessica downtown, lights, crew, and filming equipment are reflected on the car window.
Continuity mistake: When Jessica is having dinner, his glass swaps between full or almost empty depending on the shot.
Visible crew/equipment: When the cop grabs the coffee pot, a filming crew member with blue trousers is reflected on it.
Answer: It was never revealed what caused Frank's death.
raywest ★