Big zoo sleepover unlocks animal sleep secrets
4 March 2014 Last updated at 06:48 GMT
A huge experiment was carried out at Bristol Zoo to find out what animals get up to at night.
We already know that giraffes only sleep for around four hours a day, but the way different animals sleep is still a bit of a mystery.
Zoo keepers hid night vision cameras in the animal enclosures to see which animals slept the most.
They found that lions and gorillas slept for around eight hours each, while penguins kipped for just three.