An 85-pound manhole cover can become a missile when blasted out of the ground.

Exploding manholes are one of those weird and interesting side effects of living in a large city. Imagine walking down the street when all of a sudden a manhole covers flies 50 feet in the air!

In this edition of HowStuffWorks, you'll learn what causes these blasts and how they compare to the combustion chamber of a car engine.