For many of us, being half asleep is a problem solved by the morning’s first cup of coffee. But some birds and mammals use it as a strategy: literally snoozing with one eye open and with one half of the brain awake. Scientists think the phenomenon known as unihemispheric sleep allows the animals to spot approaching predators, giving them a few crucial seconds to make their escape. Now, after filming young saltwater crocodiles (pictured) for a day, researchers have shown for the first time that the reptiles also can keep an eye open when slumbering, suggesting they may have the special sleep ability, too. What’s more, after a person entered their tank, the crocodiles increased the amount of time they spent with one eye open, which they kept trained in the person’s direction, the researchers report today in the Journal of Experimental Biology. Similar observations have been made in other reptiles including lizards, turtles, and caimans, meaning that the ability could be more common among crocodilians—a group that includes caimans, crocodiles, alligators, and gharials—than was previously thought, the researchers say.