About the sharks' sleep.

Sharks don't sleep. If they don't swim, their gill slits won't be bathed with water containing oxygen and they will suffocate. However, some sharks can lie down on the ground in the coast, where there are the tides and then their gill slits are bathed with oxygen-rich water. Other sharks stay in the caves, where the current bathes their gill slits. There are a lot of such caves in the Red Sea, therefore there are many sharks. The hemispheres of the brain of sharks sleep by turns.

<em>[Good work.]</em>