Flip a distorted face upside down, and the distortion disappears

Psychologist Peter Thompson took a photo of Margaret Thatcher, rotated her eyes and mouth 180 degrees within the otherwise normal face, and found the result looked grotesque right-side up but almost normal when the whole photo was flipped upside down. The effect exposed how heavily human face recognition relies on processing features in their upright orientation; turn a face upside down and the brain's specialized face-checking machinery seems to switch off.

— Peter Thompson, Margaret Thatcher: A New Illusion — Perception, 1980