Before being wounded, the lieutenant had been dividing portions of coffee for his men with the sword. Assuming he was right-handed, he was probably using the sword in his right hand. He was apparently wounded in the right arm, and therefore switched the sword to his left hand. Generally, when the sheath is on the left side, you would unsheath it with your right hand--now disabled. He was having difficulty replacing the sword with his good, left hand. Although he was probably in shock, he recognized the need to replace the sword in its sheath, but it was virtually impossible to do so with the left hand. This entire scene, worrying about the unimportant act of replacing the sword properly after receiving a serious wound, is an absurd response to a desperate situation.