EE WAS DISMOUNTING A CATERPILLER D-11 DOZER ON UNEVEN GROUND IN NIGHT TIME CONDITIONS. WHEN HIS RIGHT FOOT STEPPED TO THE GROUND, HIS FOOT WAS ON TOP OF A CLOD OF DIRT. WHEN HE SHIFTED HIS WEI GHT TO THE RIGHT FOOT TO CONTINUE THE DISMOUNT, HIS FOOT SLIPPED OFF THE CLOD, WHICH CAUSED HIS KNEE TO ""POP"".