How Fast Is Head Nod?

A friendly head nod moves the chin at about 0.3 metres per second. Disagreement shakes can move at up to 1 m/s — three times faster, which is why a vigorous 'no' looks more emphatic than a vigorous 'yes'.

Vertical head motion almost universally means "yes" across cultures — though there are striking exceptions, like Bulgaria.

• Similar pace to baby crawling
• A vigorous head shake is 3× faster