Continuity mistake: When Jessica (a stunt double) rides her bicycle at the start, her red scarf is tied around her waist. A shot later, when the real Jessica is shown, the scarf hangs around her neck.
Revealing mistake: When Cagliostro is stabbed, there's a protruding rectangular pad under his shirt where the knife is stuck.
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.
Continuity mistake: Before Joan leaves the restaurant, she has a glass of wine on her right, but from Jessica's POV, the glass has moved to Joan's left side. Also, Jessica's glass is in front of her, but moves to the right side of the table after Joan leaves.
Continuity mistake: When Bud and Andy arrive at Cagliostro's table, Jessica stares with her glasses on, while Joan turns her head around. An instant cut later, Jessica's glasses are off and Joan is turning her head again.
Continuity mistake: When Jessica is having dinner with Joan, Jessica's right arm is either extended on the table next to the cutlery or not, depending on the shot.
Continuity mistake: When Joan leaves the restaurant, her glass is full. Next time we see it, it's empty.
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
Continuity mistake: When Jessica and the Russians escape in the Rolls Royce, the back projection is not continuous between shots. On the right side window, the place swaps between a modern city and a park. On the left window, the same people walking around are played several times.
Murder to a Jazz Beat - S1-E13
Continuity mistake: Jessica and Jonathan sit down to chat; he says, "Tastes and smells... worthy of kings and their consorts," and raises his hands. An instant cut later, from a different angle, they're lowered. (00:04:49)
Funeral at Fifty-Mile - S1-E22
Other mistake: In the end credits, Jesús is misspelled Hay-Soos, phonetically.
Revealing mistake: When Jessica is knocked down by the kids, she is replaced with a younger stunt double.
Visible crew/equipment: When Milton arrives at the airport, the filming crew is reflected in the glass on the right.
Visible crew/equipment: When Sir John Landry walks towards the fireplace before Jessica unravels the mystery, stage lights are reflected on Jessica's glasses.
Visible crew/equipment: At the beach, when Miguel jumps in the helicopter, two filming lights are reflected on the windows.
Continuity mistake: Patti and Brian enter the alley, talk to the card scammer, and keep on walking. From a different angle, they're metres behind, entering the alley again.
Continuity mistake: When Grady introduces the understudy, he puts his arm around her shoulders. A shot later, his arm is away.
Revealing mistake: When Jessica is meeting with Congressman Dan Keppner, there are two windows with the Capitol building behind. One can see it's a painted backdrop, most noticeably the window on the left with the garden view.
The Murder of Sherlock Holmes - S1-E1
Revealing mistake: In part 2 of the episode, when Jessica is mugged, Angela Lansbury is replaced with a younger and thinner stunt double twice: when she runs away and when she protects herself against the wall.
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.
Answer: It was never revealed what caused Frank's death.
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