When Glen Jeffery first took possession of a huge bag full of reindeer eyes, he didn’t really want them.

Jeffery is a neuroscientist from University College London who studies animal vision, and his Norwegian colleagues had been urging him to study the eyes of reindeer. They wanted to know how these animals cope with three months of constant summer sunlight and three months of perpetual winter darkness. “I thought it was a dumb idea,” says Jeffery. The animals would probably adapt to the changing light through some neurological trick. The eyes weren’t the right place to look.

But the Norwegians persisted, and they eventually sent him a bag full of eyes, taken from animals killed by local Sami herders. The