You're tapping your fingers against a white wall when you realize the sound you're making is actually a sick beat. You keep going and start singing along. Boo boo boop. Boo do do do doop! Finger beats!
This beat is sick, but as you tap you realize you're hacking (はく) up the wall! Slowly but surely, your fingers are hacking out little bits of the wall. And the beats don't sound as good until you move to a new, clean white area.