The ladies in this video have beautiful faces, but if you stare at the cross while the faces flash, they become distorted, even grotesque! The optical illlusion has been termed ‘Flashed Face Distortion Effect’
The effect seems to depend on processing each face in light of the others. By aligning the faces at the eyes and presenting them quickly, it becomes much easier to compare them, so the differences between the faces are more extreme. If someone has a large jaw, it looks almost ogre-like. If they have an especially large forehead, then it looks particularly bulbous.
The researchers who discovered the phenomenon, Jason M Tangen, Sean C Murphy and Matthew B Thompson, have yet to explain the cause of this interesting effect.