During the Cold War, it seems the ever-inventive CIA was up to new
tricks: sleight-of-hand, surreptitious removal of objects, secret
signals via shoelaces, slipping LSD into unsuspecting drinks from a
hollowed-out pencil, and even advice on looking stupid, and thus not
suspicious. It's all in The Official CIA Manual of Trickery and Deception, a magic manual
by magician John Mulholland that disappeared in the 1970s and has now
resurfaced. Compared to hanging suspects by their wrists in stress
positions, the era's pop-up dummies and St. Bernard costumes and radios
hidden in fake scrotums seem downright quaint. More here.
An agent "should be so normal in manner, and his actions so natural, that nothing about him excites suspicion."