How does meursault describe shooting the arab after he's already dead?

In "The Stranger", by Albert Camus, Meursault describes shooting the Arab after he's already dead as follows:

"I  knew  I’d  shattered  the  balance  of  the  day,  thespacious calm of this beach on which I had been happy. But I fired four shots more into the inert body, on which they left no visible trace. And each successive shot was another loud, fateful rap on the door of my undoing."

He describes it as knocking loudly on the door of his downfall.

c. with one finger is the answer