Thats the first thing that popped into my mind. Where I lived years ago I had a neighbor who's son was in a wheel chair. He was like that because he was working under an old pontiac lemans and the jack gave out. He finally walks now but it took 25 years to get to that point. I never gave it much thought before meeting him but it stuck with me to this day. I at least make sure I have a tire under the car if a jackstand isnt possible. I put at least something under that to keep from getting smushed.