Play a clip below, keeping your eyes on the cross in the middle (fullscreen mode works best). If you are of the sceptical kind, feel free to watch the clip again without looking at the cross to confirm that those bizarre faces are only in your head.
From TangenCognitionLab: “Like many interesting scientific discoveries, this one was an accident. Sean Murphy, an undergraduate student, was working alone in the lab on a set of faces for one of his experiments. He aligned a set of faces at the eyes and started to skim through them. After a few seconds, he noticed that some of the faces began to appear highly deformed and grotesque. He looked at the especially ugly faces individually, but each of them appeared normal or even attractive. We called it the Flashed Face Distortion Effect and wanted to share it with the world, so we put it on YouTube.”
You can read more about it, here