* The Gypsy: The initial suspicion falls on the Romani woman who was seen near the house. This sets up the expectation of a traditional, physical crime.
* The "Speckled Band": The name itself, and the strange noises from the room next to Helen Stoner's, imply a dangerous animal. This leads both Helen and the reader to focus on a creature instead of a human culprit.
* The "Speckled Band": The description of the creature as being a "speckled band" further reinforces the idea of a dangerous animal.
* The "Deadly Snake": The idea of a snake being the cause of Julia's death is planted early on, and the focus remains on this idea despite the lack of evidence.
* The "Indian" element: The inclusion of Dr. Roylott's past in India, and his knowledge of "Eastern poisons," suggests a more exotic and mysterious cause of death. This reinforces the focus on a supernatural or animalistic explanation.
All of these elements, together, create a smokescreen that effectively diverts attention away from the real culprit: Dr. Roylott himself. He skillfully uses these red herrings to create an atmosphere of fear and suspicion, allowing him to commit his crime with impunity.
The red herring in "The Speckled Band" works so well because it plays on our expectations and biases. We tend to look for simple explanations, and we are often drawn to the exotic and mysterious. Doyle masterfully uses this to his advantage, creating a story that is both suspenseful and cleverly deceptive.