The Gravity Flap

I—I crept past the napkin box toward a heavy glass jar with a domed metal cap. Right at the spout, there was this tiny steel flap dangling on a pin... what if it pinched my fingers? I hesitated, checking the quiet terrace, then reached up on tiptoe to give the lower rim a nervous poke. *Click!* It swung wide open on its miniature hinge! And when I pulled my hand back—*clink*—it swung right down and shut flush all by itself! No coiled springs, no tension... just pure gravity doing the closing work! That’s... that’s completely brilliant for a lid, isn't it?