Crosswords and Intelligence Agencies.
There is that lovely story of a leading WW2-era newspaper crossword compiler being a master at a boarding school. The school was based near an American base in England. The security agencies were concerned because words associated with the secret planning of D-Day were appearing as answers in the crosswords this school master set. The agencies had to consider if this was coincidence, conspiracy, or if boys at the school picked up on words being used by the nearby US servicemen and repeated them in the school, thus subconsciously influencing the crossword compiler.