Say "Ahhhh" in your deepest voice. Then say "Ahhh" in your highest pitch voice. Then say "Ahhh" while transitioning from your deepest voice to your highest pitch voice, then go back down to your deepest voice again.
That's an exaggerated example. To achieve a proper bounce, you only need to fluctuate the pitch of your voice a tiny little bit. It can make you seem ridiculous if you overdo it.