TIL that in world war 2, English soldiers would use passwords that had sounds that the language of the people they where fighting against did not have, so that they could tell if an unidentified person was an enemy soldier tying to infiltrate them by if they said these sounds correctly.

https://en.wikipedia.org/wiki/Shibboleth#:~:text=%5B12%5D-,Some,-American%20soldiers%2…
#til #todayilearned
https://www.reddit.com/r/todayilearned/comments/1g1a2r6/til_that_in_world_war_2_english_soldiers_would/