Was watching a new episode of Western Extreme yesterday and they showed a new broadhead. I don't remember the name, but basically it is built into the nock and has a sleeve with your fletches on it. When the fletches hit the animal the sleeve comes off and the 8" blades are exposed and opened up. Did a good job on the warthog he shot. So you pretty much have 2 broadheads on your arrow as long as you get a pass through.
Pretty cool idea I think.