How do I say this

Explain this sound?

This shushing and slipping and sliding sound

Of black, clouded gray, wiping chalk off the board.

How joyous; how refreshing; how nice!

Smoothly flowing, yet jerking ruggedly.

A blackboard eraser, the professional kind,

Or just an old sock torn a hole through the rind,

Wiping the white

Off the green-black board.

So annoying, though! When the job is done,

When the words are all gone and the kids are all run,

Boof! Paf! Phom! Powdery white goes flying

Like a lady's pale foundation.

I hold my breath to keep the dusty stuff

From getting in my throat and lungs

And making me cough and sneeze and tear a little.

Yet still it gets there

As I'm cleaning out the brush.

Isn't it so

Annoying? Such a wonderful thing!

Of erasing the words written on the screen.

Yet then, Phom! That's the price you pay,

The terrible white dusk flying in your face.