Don’t worry! It’s not dangerous.
Maybe most of you seen already this strange hole in the plane’s window. But what is its really purpose?
They have a very important role in maintaining the cabin pressure in normal parameters. As we know, a plane window contain three layers of glass.
First layer is the strongest of them all. It is made of glass and acrylic. The hole is situated on the middle layer of the glass, being destinated to maintain the pressure between the first layer and the third one.
If the third layer ise destroyed by accident, the first one will be strong enough to not break and maintain a normal pressure. This means the pilot can safely take the plane to a lower altitude or even to land it.