Horse

Horses have been humanity's closest working animal for thousands of years, yet most people don't know that they can recognize human emotional states from photographs alone, have the largest eyes of any land mammal, or that they're standing on the equivalent of a single enlarged toenail. These are not obscure creatures — they're deeply familiar ones with almost entirely unknown inner lives.

Facts you didn't know

• 1

  Horses recognize human emotions from photographs of strangers they've never met. When shown photos of angry human faces, they display stress responses. When shown happy faces, they approach. The recognition applies even to static images with no context beyond facial expression.

• 2

  Horses have the largest eyes of any land mammal. Their visual field covers nearly 350 degrees — they can see almost completely around themselves simultaneously. The only blind spots are directly in front of their nose and directly behind their tail.

• 3

  Horses can sleep standing up using a 'stay apparatus' that locks their legs, but they can only enter deep REM sleep lying down. A horse deprived of the ability to lie down will eventually develop a sleep deficit that manifests as narcoleptic episodes — suddenly collapsing mid-stride.

• 4

  A 2015 study identified 17 distinct facial movements in horses — more than chimpanzees (13), comparable to humans (27). These expressions regulate social relationships within the herd and appear to communicate specific emotional states.

• 5

  A horse's hoof is a single digit — the middle finger, evolutionarily speaking. The side toes gradually reduced over 55 million years of horse evolution, leaving modern horses standing on the tip of one enlarged, thickened toenail. The hoof is a fingernail.