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.
The Return of Sherlock Holmes (1986)
1 revealing mistake in The Abbey Grange
Starring: Jeremy Brett, Rosalie Williams, Edward Hardwicke
Other mistake: It's not possible for Holmes to remove all of his elderly bookkeeper disguise in the mere seconds Watson turned his back.