and stop, the skull stops almost immediately, but unfortunately the brain doesn't. and that moving back and forth, that reverberation is the villain here. >> and you mentioned all of these various, you know, propositions including the sideline exam. as advisers to the nfl, how do you enforce that? because there is this culture as you mentioned playing through it, it's a competitive sport. are there going to be penalties? how do you make sure it happens? >> i think the players certainly with the tragedy, the terrible tragedy this week, they're pretty attune to the fact that, you know, something has to change. no one wants a long-term problem after they've suffered multiple concussions. so i think you're going to see a culture change actually enforce among the players and the fans. they're going to insist on it. i think there are going to be rule changes, and that's above