There's also the method of using slang/phrasing that's obvious to your own side but the captors might be oblivious to, as in the North Korean captive example:

There's also the method of using slang/phrasing that's obvious to your own side but the captors might be oblivious to, as in the North Korean captive example: "Bucher was psychologically tortured such as being put through a mock firing squad in an effort to make him confess. Eventually, the Koreans threatened to execute his men in front of him, and Bucher relented and agreed to 'confess to his and the crew's transgression.' Bucher wrote the confession since a 'confession' by definition needed to be written by the confessor himself. They verified the meaning of what he wrote, but failed to catch the pun when he said "We paean the North Korean state. We paean their great leader Kim Il Sung" ("We paean" sounds almost identical to "we pee on").[4]"