My favorite secret ink story is about a Nazi spy who secreted invisible ink in his tooth. It’s probably my favorite because one of the most intriguing aspects of the history of secret writing is the inventive way in which people concealed their materials.
Of course, hiding invisible ink in a tooth is one of the more bizarre concealments, but it’s a good one because border control agents usually don’t ask people to open their mouths for inspection. Even if they did, there is no reason they should suspect a filled or capped tooth contains invisible ink or poison or other dangerous things spies put in their teeth.
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