Chuck Norris doesn’t sleep, he waits. So, it seems, do crocodiles.
According to a new study published this month in the Journal of Experimental Biology, crocodiles sleep with one eye open, leaving the other to watch for prey and threats.
Researchers from La Trobe University in Australia used infrared cameras to monitor crocodiles day and night at an aquarium. When a sleeping croc was in the presence of a human or another crocodile, its open eye would follow the potential threat, leading scientists to believe that the crocodile’s entire brain was not asleep.
Scientists believe the crocodiles are practicing what is known as “unhemispheric sleep,” where only one side of the brain shuts down during sleep. Similar behavior has been observed in cetaceans and birds.
Though what scientists see is consistent with unhemispheric sleep, they would need to monitor a croc’s brainwaves to make a conclusive determination. This would involve placing electrodes onto crocodiles’ skulls, not the easiest of experiments.
If crocodiles do indeed only shut off part of their brains for sleep, it suggests that the complete sleep of humans and other terrestrial mammals may be unusual, even unique, in the animal kingdom.