Trope-a-Day: Something Only They Would Say

Something Only They Would Say: A number of intelligence agencies and other organizations use this kind of call-and-response code as a non-technology-dependent shibboleth, but for the sake of extra security, they’ve more or less perfected the technique of embedding them into subconscious levels of the mind-state, so that the person using them doesn’t actually know what they are to give them away, even under duress.