Alexandra Schnell receives funding from the Royal Society. A couple of years ago an octopus named Heidi was filmed changing colours as she slept. The footage shows her flickering from a ghostly shade ...

For humans, sleep is a necessity, a mystery, and a luxury. It’s not known why we need it but we do—and an hour more or less of it can make your day either great or grumpy. Most animals sleep, too, ...