Literal translation: It is the space inside that gives the drum its sound.
Figurative translation: It is the empty-headed one who does the most talking.
Read. Ponder. Visualize. Snicker. This ʻōlelo noʻeau makes total sense to me, kumu hula that I am. A drum is a good comparison to one who is empty headed (though I place very high value upon my pahu hula-hula drum) while not so much to the empty headed person.
I love a good ʻōlelo noʻeau that has thoughtful (and funny) figurative language. Lately on the tv there are a few pahu sounding out (think campaigns). Who are the people you deal with on a daily basis that you can liken to a pahu? They talk talk talk but not much coming out. It doesn’t take long for us to figure out who is ʻolohaka, or empty. They may have good kani, sound, but just like the pahu, they are hollow inside.