That you get when you crack your knuckles.

If the joint is pulled apart slightly, the fluid can no longer fill the space and a vacuum bubble will form. This will make a noise when it collapses. The process is very similar to cavitation in propellers that move liquids.

I'd only known about four.

There are a handful of people in the world who can remember everything that they experienced, even when a baby.

Fortunately for everybody around me, senility has long since set in.

That's one I still hear often.

Many people are convinced that it makes kids hyper. I try to explain the Hawthorne effect to no avail.

Also learning styles.

It's very annoying that so many people buy that one.