Suppose you are a clandestine service agent for the CIA and you need to tell another agent that you have important information for him, but you suspect the walls have ears. Well, you could tie your shoelaces in a pattern like the one shown below, and your message would come out loud and clear without your speaking a word.

The illustration is from a new book called "The Official CIA Manual of Trickery and Deception," based on two manuals written by professional stage magician John Mulholland. During the Cold War, the CIA hired Mullholland to teach their covert operatives sleight-of-hand tricks and secret signals they could use in the field. The manuals explained tricks like how to drop something or pick something up without arousing suspicion, or how to pass a pin or a pill concealed in a matchbook while pretending to be simply offering a light.

For a trick to be good, said Mulholland, it "must be simple in its basic idea”, and if you practiced relaxing your facial muscles, "the greater the effect." Mulholland's classified manuals were supposed to have been destroyed in 1973, but a copy was discovered in 2007 among declassified CIA archives by intelligence historian H. Keith Melton and retired CIA officer Robert Wallace, who wrote the historical overview for the book. Rather than a dashing, James Bond-type figure, Mulholland described the ideal agent as anonymous, bland, and “so normal in manner, and his actions so natural, that nothing about him excites suspicion.” At least until his Russian counterpart glanced at his shoes.

Hat tip Kottke.org. From the Boston Globe article by Tom Scocca; illustrations by Javier Zarracina/Globe Staff Graphic