Uh... so... basically...

The 'balls' are a man's most tender spot. They're very sensitive, so even if you hit them just a little, it'll hurt.

They're so weak, you could crush them unexpectedly easily, even with just a woman's strength.

If you do crush them, it's entirely possible he'll just die from the pain!

The specifics are taught in health studies, but...

They're a man's most precious place, so you can't be too rough with them!