I did this with my brother the other day. So many bricks were shat.
Compound bow + piece of cotton + gasoline + matches
Everyone has to try this. I'd wanted to do this my whole life and I can't get over have freaking awesome it is watching a flaming arrow fly. And it makes the most amazing sound ever.
Protip: Do it with a friend and take turns shooting at each other and dodging. It's a real rush. Just though I'd share.