This is a basic prototype of a way to trim down fingernails with one hand. There is a toilet paper roll covered in 220 grit sandpaper attached to a hand drill.
*Update: A way to actual do this with just one hand by having a device (the purple thing) that spins on its on when you push a button. It is held into place with the box and the sand paper/toilet roll is super glued on there to spin when you push the button.
