When Nero is killed and falls from the boat, he is holding his sword in his right hand. But during the fall, his sword moves to his left hand and is then released to fall into the water. As he impacts the river, the sword has returned to his right hand.
During the fight on the boat, after Nero is fatally stabbed, he has a hole in his shirt and dribbles blood down it, staining it. However, when he falls off the boat, his shirt appears clean and unpunctured.