My first thought, too. All those unsealed tiny gears. One fragment of metal filing in there? Perhaps a cascade failure of teeth chipping and flinging fragments

My first thought, too. All those unsealed tiny gears. One fragment of metal filing in there? Perhaps a cascade failure of teeth chipping and flinging fragments until total breakdown. Reminds me of the head of a waterpic toothbrush - a packet of tiny gears, the weakest point in the device, constantly wearing out.