&quot;In 1919, a tank of molasses in Boston collapsed. Molasses is thick, so you might think it would flow out slowly, but it didn&#x27;t. The wave of molasses swept down the streets too fast to outrun, demolishing buildings and killing 21 people.&quot;<p>From (<a href="https:&#x2F;&#x2F;what-if.xkcd.com&#x2F;111&#x2F;" rel="nofollow">https:&#x2F;&#x2F;what-if.xkcd.com&#x2F;111&#x2F;</a>), where I originally learned about this event :P