4 things you can literally learn while you sleep

When you go to sleep tonight, put a book under your pillow. When you wake up tomorrow morning, you'll have its contents memorized.

Ok, so that probably won't work.

But don't lose hope just yet: It turns out there actually are a few things you can learn - or at least improve your grasp of - while you snooze. Most of them depend on one thing: Sound.

Here are some of the skills you may be able to sharpen in your sleep: