EMPLOYEE WAS OPERATING MANTRIP. THEY DID NOT REMOVE TIMBER FROM THE BACK OF THE VEHICLE. THE ROADWAY WAS MUDDY AND ROUGH. THE VIBRATION OF THE VEHICLE CAUSED THE TIMBERS IN THE BACK OF THE MAN TRIP TO SHIFT. THE END OF ONE TIMBER CAME IN CONTACT WITH THE RIB. THIS CAUSED THE OPPOSITE END OF THE TIMBER TO SWING AROUND, STRIKING HIM ON SIDE OF HIS FACE, JUST BELOW THE RIM OF HIS HARD