It turns out that itsy bitsy hole in the bottom of your airplane window is actually a very important safety feature. It’s all-too-easy to let your mind wander when you’re confined to a tiny box of space while hurtling 40,000 feet in the air at hundreds of miles per hour, but rest assured: every single window on the airplane has the same hole.
More officially, it’s called a breather hole and it’s used to regulate the amount of pressure that passes between the window’s inner and outer panes. In short, the system ensures that the outer pane bears the most pressure so that if there were a situation that caused added strain on the window, it’s the outside panel that gives out (meaning you can still breathe).
The breather hole also keeps the window fog-free by wicking moisture that gets stuck between the panes. After all, half the fun of an airplane ride is the in-flight scenery shots. Mystery solved.