 Okay, fun fact. Did you know that semen can be used as invisible ink and that the spies in World War I actually used it for their secret comms? Apparently the head of MI6, which is the British Secret Service, discovered this in 1915 right in the middle of World War I. The troops in the trenches didn't always have access to vinegar or lemon juice or all those other wonderful things that are needed to make invisible ink. But semen worked the same way and of course semen was always handy. In the end, however, they didn't use semen for secret comms for very long because they discovered that it made the letter smell really foul. Apparently stale semen smells horrible. But it's always useful to know, right? Just in case.