If you're ranking fun things to put in a balloon, helium probably tops the list, followed probably by water and then plain old human huffin' and puffin'. But a fascinating thing happens when dry rice is poured into a balloon and all the air is sucked out: welcome to your new favorite filler.
First, the grains—or glass marbles, or pinto beans, or spiral pasta—are funneled in to a custom-made sac, and the air is vacuumed out. The remaining latex-covered lump is solid but malleable, perfect for molding into a bowl-like shape.
A little plaster is poured into the hollow, then swirled around before it's left to dry. When the air is let back into the balloon, the brand new cast can be removed and voila! It's a one-of-a-kind decorative vessel.