"In literature, a red herring is a narrative element intended to distract the reader from a more important event in the plot, usually a twist ending. The term “red herring” originates from the tradition whereby young hunting dogs in Britain were trained to follow a scent with the use of a “red” (salted and smoked) herring (see kipper). This pungent fish would be dragged across a trail until the puppy learned to follow the scent. Later, when the dog was being trained to follow the faint odor of a fox or a badger, the trainer would drag a red herring (which has a much stronger odor) across the animal’s trail at right angles. The dog would eventually learn to follow the original scent rather than the stronger scent."
— Red herring (narrative) - Wikipedia, the free encyclopedia