Have you ever wondered why do ballpoint pens have a little hole on the side? It turns out, there is a good reason for it. For example, if you’re travelling on a plane and the air pressure changes, without this little hole your pen could ruin your trip by leaking in the pocket of your favorite jacket or literally exploding. Often we don’t realize how thoroughly thought through are the technologies behind some objects that we use on an every day basis. Even a common pen has a couple of secrets. So, here are 10 everyday things with unexpected functions.