throw off, or throw off the scent. var. put off the scent. To misdirect or to distract or divert from pursuit or attention with a “red herring.” That is, to deliberately mislead investigators or pursuers.

The shortened phrase “throw off” is linked by the OED to fox hunting; add in the word scent and the canine reference is inescapable. Dogs' noses are many times more sensitive than humans'. Studies have found that dogs can detect some chemicals at concentrations hundreds of times less than people are able to. Stephen Budiansky speculates that “for other compounds the dog's edge may be a factor of a million or more.” He offers a tale that speaks of how much dogs rely on their sense of smell.

The scientists first tried…having a person walk either forward or backward across pavement or grass. Twenty minutes later, a trained tracking dog and its handler, neither of whom knew which way the person had actually walked, were allowed to approach the midpoint of the track and the dog was set to work. The dogs consistently were able to follow the trail in the actual direction the person walked, regardless of which way the toes and heels were pointing.

So to throw a dog off the scent is a pretty good trick. Indeed, films and television narratives about escapes, whether of criminals, slaves, or prisoners, often show the attempts by those fleeing to throw the bloodhounds off the scent, most frequently by entering flowing water of some kind.

Variations on the full phrase appear in works by such writers as Moliere, Tolstoy, and Goethe.

The most common metaphorical strategy for throwing someone off the scent is to use one or more “red herrings.” A red herring is “a clue or piece of information which is or is intended to be misleading, or is a distraction from the real question.” As long ago as the 16th century dried smoked herring was used to train hounds to track. The idea of using red herring to create a false trail probably originated in an 1807 story by W. Cobbet.

About the illustration: Figure 1 shows fictional police detective Bobby Goren—cast as a modern day Sherlock Holmes—using his preternatural sense of smell in pursuit of a criminal. This image is excerpted from a promotional still photograph, and the copyright for it is most likely owned by either the publisher or the creator of the work depicted. I believe that the use of scaled-down, low-resolution images of promotional photographs to provide critical commentary on the work in question qualifies as fair use under United States copyright law.

Figure 2 shows Lord Peter Wimsey—portrayed as somewhat of an interbellum Sherlock Holmes—contemplating the Five Red Herrings in the Dorothy Sayers book of that name. This image is excerpted from a promotional image, and the copyright for it is most likely owned by either the publisher or the creator of the work depicted. I believe that the use of scaled-down, low-resolution images to provide critical commentary on the work in question qualifies as fair use under United States copyright law.