Mario Paint is chock full of stuff to play around with. Even the title screen can keep you occupied for a while.

Just click on all the letters for different effects:

Click on the "P", though, and you get this tranquil scene.

Each thing wandering around on the screen has a different sound associated with them, none of them too exciting, but all of them kind of silly. Occasionally, though, you see a star fly by.

It's real hard to click on, because it moves so fast. I have the best luck if I position the pointer on its path ahead of time (it goes the same way every time), and then click as the star passes underneath. What happens if you do?

Stuff starts raining down from the sky and some kind of harp-like music starts to play.

And now you know what the star does, lucky you.