Biting soda can.

I shook a can up a shitload and then rolled it down this huge hill in my neighborhood. It kept hitting the curb until it sprung a little leak and started spraying a little tiny stream... so I picked it up and threw it down as hard as I could. It exploded with a sound that was identical to a shotgun blast and sprayed a huge splatter across the road... not to mention the fact that the can nearly blew into two separate pieces. It was pretty cool.