On Thursday morning, a St. Louis couple left a YMCA gym and discovered that their car was conspicuously missing from its spot. Upon further investigation, they realized it was actually still parked there—only it was 20 feet underground, swallowed up by a sinkhole

However terrifying they may be, sinkholes aren't that unusual in Missouri; the state is home to at least 15,000 of them, and it's had sinkhole-related regulations since 1853. That's nothing in comparison to Florida, though, which has the most sinkholes in the U.S. There's even a company that bills itself as the Sunshine State's "most experienced residential sinkhole repair company."

So what causes sinkholes to form, anyway? YouTube’s Practical Engineering, led by civil engineer Grady Hillhouse, set out to put this question to bed by creating a miniature replica of a sinkhole.

The common denominator in both instances of natural and human-created sinkholes? Water. Not unlike the natural process that causes caves to form, many of the human-made sinkholes in recent memory have been the result of pipes leaking and causing internal erosion of the soil. This process leaves all but the roadway acting as a "final bridge" above the deep, dark void. You can probably guess what happens next. Watch the full video below: