Sullivan’s son was a guest in a truck driven by Crabtree (D). The truck was a large trailer-tractor truck owned by Hoover Motor Express Company, Inc., and used by it in its business as a carrier of freight. D was driving the truck with a load of freight from Nashville to Atlanta, and he permitted the son to ride with him as a guest in the cab of the truck. The road on which he was driving was a paved first-class Federal-state highway (U. S. 41, Tenn. 2), but coming down the mountain from Monteagle to Pelham it had a number of moderate grades and pretty sharp curves. It was mid-afternoon, and the weather was dry and clear. As D approached a curve, another truck overtook D and passed him. D's truck suddenly swerved from his right side over to his left, D's ran off the left shoulder, overturned down a steep embankment, and crushed their son to death. P contends that D was guilty, as a matter of law, of negligence in causing the death. P’s brought an action against D for the death of their son. At trial, D stated that gravel on the road or the broken pavement might have caused him to lose control of the truck. D also speculated that his brakes or some other mechanical part on his truck may have caused the accident. The only certainty in D's testimony was that he was not certain about the cause of the accident. The verdict was given to D and P appealed; res ipsa loquitur applied to the facts of this case.