One Weird Visual Illusion Explained
Begin by taking a regular sheet of white printer paper. Any color will do. Roll it into a long, narrow tube, about the size of a quarter. Make sure both ends remain open so you can see through both ends as shown below.
Look through the tube with one eye. While keeping both eyes open, bring the palm of your hand close to your other eye, an inch or two away. Slowly bring the palm parallel across your eyes until it touches the tube of paper. As you do this, you should see a hole appear in your hand! Obviously there is no hole in your hand but a cool little illusion trick nonetheless!
Why is this happening? I'll point you to the video link above for details. BrainCraft does a much better job explaining than I ever could!