First (sensible) try at a half shell for these shakers. You'll need to print a minimum of four to make a single set; eight shells makes a two-hand set.

These are sized for quite small hands and for narrow (~ 5 mm braided black dacron) rope. Please adjust accordingly.

You probably want to print this with a non-brittle filament at close to 100% fill. You must use support.

Toasted barley might make a good filling. Glue the halves together, thread the string through and make it long enough that you can swing the shakers round the back of your hand.

And no, I can't do this, either. Link via MeFi.