Saw these earlier today on AT, and didn't think much of them. The are designed to pass through the animal, then come apart and entangle the animal, preventing it's escape.
Here's the site to them:
http://www.thetangler.com/
And here's a video they have (caution, not for the meek):
http://www.youtube.com/watch?v=FoTbDx90768
I personally think they could've chose some better advertising footage, and don't think these BH's would be legal in many states, your thoughts???