TIL the US government recalled and burned $200m in currency and printed special money for Hawaii in case Japan invaded [source, comments]

TIL during the gulf war an American F-15 dropped a bomb through an enemy helicopter that was attacking friendly forces [source, comments]

TIL the fictional languages in the Game of Thrones series are fully complete languages. Of all the actors that had to speak one or more of them, the person that portrayed the Grey Worm character was considered the best/most talented. He was skilled enough to speak like a natural native speaker. [source, comments]

TIL that 2 million discarded tires were deliberately dumped off the coast of Florida in the 1970’s, with the intent to stimulate growth of new coral reefs. Instead, the tires ended up killing off nearby reefs. The tires are still causing damage today. [source, comments]

TIL Leonhard Euler wrote 234 letters to 15 year old German Princess Friederike Charlotte over a period of two years in order to teach her math, physics, and sciences. These letters were later reprinted as a textbook for "every female academy in the kingdom" [source, comments]

TIL cars at the turn of the 20th century were more aerodynamic in reverse. They learned this after Chrysler hired Orville wright to create a wind tunnel for them [source, comments]

TIL 25000 disabled people were sterilized in Japan between the 1950s and 1990s, at least 16,500 forcibly [source, comments]

TIL that Andrew Johnson is the only United States President to serve as a senator after his term as president, with his term as Tennessee Senator lasting from March 4, 1875 until his death on July 31, 1875. [source, comments]

TIL Ciabatta bread was only recently invented in 1982 [source, comments]

TIL that if you drive at 45 mph on a specific stretch of Route 66 in New Mexico, the road's rumble strips will play 'America the Beautiful.' [source, comments]

TIL that, on April 6, 1994, the presidents of Rwanda and Burundi were both assassinated when their plane was shot down. In Burundi, it was seen as a tragic accident and their president was in the wrong place at the wrong time. In Rwanda, it set in motion the Rwandan Genocide. [source, comments]

TIL because of the 1994 Dietary Supplement Health and Education Act, dietary supplements in the US don't need to be approved for safety, don't need to disclose side effects, and don't even need to contain listed ingredients [source, comments]

TIL that comedian Jon Stewart is a passionate advocate for 9/11 first responders and helped get the James Zadroga Act passed, which provides affected first responders with 75 years of health coverage and five years of compensation. He also fought for it's reauthorization in 2015 and 2019. [source, comments]

TIL that heirs to the throne of the Ottoman Empire were kept under house-arrest in the "Cage" from puberty until death (or becoming sultan), and it was common for a new sultan to have his brothers killed, including infants, sometimes dozens at once, to reduce the number of claimants to the throne. [source, comments]

TIL the boy whose exorcism inspired "The Exorcist" later became a NASA engineer, where his contributions significantly supported the Apollo missions during the 1960s. [source, comments]

TIL that Roger Corman, director of low-budget movies, helped kick start the careers of Francis Ford Coppola, Martin Scorsese, James Cameron, and Ron Howard. He reportedly told Howard: "If you do a good job on this film, you'll never have to work for me again." [source, comments]

TIL that the first webcam was invented to monitor a coffee pot at the University of Cambridge, allowing researchers to see if the coffee was ready without leaving their desks. [source, comments]

TIL that serotonin, commonly linked to happiness as a neurotransmitter, has a surprising dual nature: it can be toxic. When injected into the skin, it causes severe pain and is a key component in wasp, hornet, and scorpion venom. [source, comments]

TIL Approximately a billion people are infected with the roundworm Ascaris [source, comments]

TIL Benjamin Franklin turned a rival into a friend by asking him for a favor and thanking him later. This is called the "Benjamin Franklin Effect". [source, comments]

TIL that an Australian man survived a wildfire by scuba diving in his friend’s pool while the fire raged around him [source, comments]