Factual error: When Holmes is on the mantelpiece to examine the cut bell rope, you can see a telephone line against the wall; it has been nailed to the top of the wainscoting with two standard white cable clips.
Revealing mistake: While Holmes and Watson are investigating the crime scene, there is a shot of them that shows the dead man's hand. His hand is visibly shaking, revealing the actor is struggling to maintain the position of his hand.
