OceanMarine Mammals
Dolphins sleep with half a brain at a time.
One hemisphere shuts down while the other keeps them surfacing to breathe.
Source
This fact is written from the English Wikipedia article it links to, so you can check every word in one tap. Fact Drop rates that source 4 out of 5 for credibility, and the rating travels with the fact on the back of its card in the app.
Why it sounds fake
What most people think
Sleep is all or nothing, and an animal that lives in water must somehow not need it.
What is actually true
Half the brain sleeps while the other half runs the one job that cannot wait: breathing.
More ocean facts
Ocean facts from a place we have mapped less thoroughly than Mars. A male anglerfish merges with his mate for good, there are lakes at the bottom of the ocean, and below about 8,400 metres there are no fish at all. Each fact links to its source.
- Whale songs go through fashions.
- Ambergris forms in a sperm whale's gut and is found floating or washed up on beaches.
- Sea otters have pockets.
- A blue whale's tongue weighs as much as an elephant.
- The finest candles were pressed from spermaceti, the waxy oil filling a sperm whale's head.
- A sperm whale's click is the loudest sound any animal makes, and it is produced by a nose.