When a murderer plants a knife in someone else's home to try to throw the police off track, the knife is an example of a red herring.
"Up in the morning, and had some red herrings to our breakfast, while my boot-heel was a-mending, by the same token the boy left the hole as big as it was before." (Samuel Pepys diary entry of 28 February 1660)
Origin of red-herring
- Sense 2, probably from the use of smoked herrings to lay scent trails for hounds to follow
From American Heritage Dictionary of the English Language, 5th Edition
- It originated from a news story by English journalist William Cobbett, c. 1805, in which he claimed that as a boy he used a red herring (a cured and salted herring) to mislead hounds following a trail; the story served as an extended metaphor for the London press, which had earned Cobbett's ire by publishing false news accounts regarding Napoleon.
- Until 2008, the accepted etymology of the idiom was that red herring were used to train dogs to track scents. This has proven to be a false etymology.