The Platypus used to be considered a myth like Bigfoot and the Yeti.
18
In 1518, a "dancing plague" struck Strasbourg, Alsace, whereby hundreds of people danced fervently in the streets over the period of a month. Some suffered heart attacks or strokes, and many others died from sheer exhaustion. It remains unexplained.
19
There is a mysterious and loud radio signal known as 'the space roar' that has yet to be explained.
15