We all know about the red herring in the plot of a detective novel, the misleading suggestion of a perpetrator and motive for the crime, to throw us off the scent of the real killer. Red herrings, colored by the process of salting and smoking, were a cheap food in the Middle Ages and had a particularly strong smell. The belief is that they were used to mislead hunting dogs. From this practice came the meaning of a false scent. Learn the origins of some more phrases we use all the time.