I have to say I’m grateful that my classmates in school never discovered the mess-generating superpower of felt-tipped markers. As the Slow Mo Guys demonstrate here, when you spin or fling these markers, ink will stream out of them. That’s due, in part, to the air vents present near the tips. Markers (and other pens) have those to equalize the pressure between the outside and the ink reservoir; otherwise, the ink won’t flow to the felt tip as it should. Is anyone else surprised by the sheer volume of liquid ink apparently contained in these pens? (Image and video credit: The Slow Mo Guys)