1HOLES IN THE AIRPLANE WINDOWS
Look closely at an airplane window and you’ll spot something weird: a little hole in the bottom. Take an even closer look and you’ll realize that unlike other windows, this one is made of three panes, and the hole is in the middle one. The quirk is there to protect against the pressure drop of flying high into the atmosphere, according to Slate. As a plane ascends, the pressure outside drops massively, but the cabin is designed to stay at a comfortable pressure. That leaves a big difference in pressure inside and outside of the plane. The outside window takes on most of that pressure, and the hole in the middle one helps balance the pressure difference. The inner window is just to protect the middle one.