The pitch drop experiment has been running for almost a century.
Why it is true
The pitch drop experiment began in 1927 at the University of Queensland in Australia, to demonstrate that pitch, despite appearing solid, is an extremely viscous liquid. Only nine drops have fallen since it began.
Source: University of Queensland
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.