Why does it kill you if a car runs over you? (yes, I'm serious)?

I've thought about this for a long time, and I'm sorry, but I guess I'm just not getting it. If I lay down in the street long ways with my arms to my side, and a car comes down the street and runs right over me (straddling me as it goes over), where I'm right in the middle of the tires, what kills me? I don't understand. Is the heat so intense under the car that it burns me to death (from tangled web of exhaust pipes under there), or is it some pressure wave that's present under the car (I'm not a physics major or anything, so I don't know how else to describe it)? I've never really figured out exactly what would kill you if a car ran over you like that. I'm really getting frustrated because no one I know really seems to know the answer. Help.