A red herring is a ploy to deceive or throw someone off the scent and therein is the derivation, from the training of hunting dogs. In the 17th century, dog trainers, especially in Scotland, would draw a smoked herring across a hunting trail in order to sharpen the dogs’ senses. These smoked herrings were reddish brown in colour, hence known as red herrings. Sometimes of course, the smell of the red herrings would have the opposite effect and put the dogs off the scent, but really well trained dogs would eventually pick up the true scent again. By the 19th century, the current figurative meaning of a deceptive ploy had been so well established that its origin in training hunting dogs became largely forgotten.