Red Herring

A herring that has been dried, salted and smoked turns a reddish colour. These cured fish have a particularly strong smell, so in medieval times they were useful as a lure for training hounds in stag hunting.

Later, people who were opposed to fox hunting would drag a red herring across the fox’s trail and entice the hounds away from the scent of their quarry. So a red herring was something to put you off the scent.
A red herring as a metaphor is anything used as a distraction to draw attention away from the central issue.