The fastest-moving muscle in the human body is the orbicularis oculi. Humans have two of these, one in each eye, and they control the closing action of the eyelids. When the corneal reflex (an involuntary reaction that protects the eye) is triggered – such as an object touching the eye – the orbicularis oculi snaps the eye shut in less than 100 milliseconds (0.1 second).
Although we understand the physical mechanism by which we blink, we’re still not entirely sure why we blink. Researchers investigating the phenomenon of blinking have noted all sorts of odd patterns – babies blink less often than adults, women blink more than men, people watching movies blink in unison – but don’t have any clear understanding of the underlying cause.