fresh operation

A code for "jerking off" by british spies during the 1940s. Semen is a very effective invisible ink. Like other invisible inks, semen is undetectable when it dries out, but it has one big advantage over its competitors it doesn't react to iodine vapor. Since iodine vapor was the main detection method for invisible ink during the war, writing code in semen meant that even if a message was intercepted, its secrets most likely wouldn't be revealed. This technique was actually used in the field, where only one flaw was found: its distinctive smell. While fresh "ink" apparently didn't give off too malodorous a scent, one spy in Copenhagen stored his jam in jars, causing his letters to "stink to high heaven," and was told that a "fresh operation" was necessary for each communique.