Really not sure of your angle here, I don't own a prius or a smart, but no car is invincible, not even the smart. I don't want to go down the whole safety comparison, folks get all wound up about it as it is, and I think lightweight is a virtue indeed.
But no crumple zones in a smart and you bounce off of other cars, and subject the passengers to greater decelerations.
The good stuff starts about 0:55