AMAZING illusion. Watch fullscreen if possible. Feel free to pause at any point and confirm the faces are not actually deformed.
Our eyes do a bad job at interpreting reality, the brain invents stuff all the time. Optical illusions are the result of the brain trying to make shortcuts and interpret what it is seeing, but failing. There is a spot in the eye where light is not registered, yet you don’t see a black spot when you look at something. Your brain covers it up. There are so many other examples of optical failures we encounter every day; if you are interested, google it! Motion parallax and saccade are good places to start.