The substitution of an aleph א for the chet ח in Abel חבל creates a pun in the riddle. [1]
↑▸±Ge 4:10 And he said, What hast thou done? the voice of thy brother’s blood crieth unto me from the ground. [{blood: Heb. bloods }] }}
Abel הנל was appropriately named: become vain, empty, breath, Abel. His life became vain when Cain slew him. [1]
↑▸±Ge 4:8 ¶ And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
