The internet is full of millions of different optical illusions, be they challenging people to find the hidden animal or object in a picture or pictures that are often difficult for the human eye to correctly comprehend. They are known for driving internet users crazy and this one is no different.Unless you've been living under a rock for the last decade, we have all already seen many of these optical illusions, but it is often difficult to reproduce them at home when you want to impress your friends.This illusion on the other hand is easy to recreate. It is done using a piece of paper and a glass of water which is half full - or half empty depending on your philosophical outlook on life. As you can see, the water in the glass changes the direction the arrow is pointing as it passes by. A quick and easy illusion, but quite mind-blowing nevertheless!And if you're interested in optical illusions and are looking for a good challenge, why not check out this man's incredible optical illusion videos!