of how the changes are made to the cars and it was to prevent exactly what susan was saying, deacceleration with these unbelievable impacts. there is a fact you can do that. >> and they're available. in the next slide, we see, after a concussion -- a concussion is not like a bone fracture where it's all over in an instant. it's actually the beginning of a progression of symptoms, some lasting minutes, some hours and some days. what we see is there are energy needs that change over time, the glucose metabolism, the cerebral blood flow which provides important nutrients to the brain and oxygen which is decreased after concussion, and if a repeated concussion occurs in the setting in an already compromised brain, then the response to the very same brain deformation could be dramatically difference. the way tori told us about her symptoms of a subsequent concussion or the next day when you've had a subsequent concussion, that's consistent of an injury on top of another injury and that's devastating with worsening and more long-lasting symptoms. so if in doubt, sit it out. you should not go back