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Elephants never forget, but new research proves that their talent is even more impressive than scientists realized.

Researchers at Wits University in Johannesburg put Fitbit-like devices on two wild female African elephants to track their sleep, by gauging when their trunks stopped moving for several minutes or longer. They discovered that the elephants slept much less than they’d anticipated, sometimes going almost two full days without actually resting.

Watch the video above for more details about how little elephants sleep, why that’s the case, and how the findings could disrupt what we thought we knew about the nature of sleep more generally.