When Sean Penn is outside the motel with the gun, he fires three shots past Benicio Del Toro's head into the ground behind. When Benicio falls to the ground you can see an ear plug in his left ear.
The experiment that showed that humans lose 21 grams at the moment of death were later shown to be highly flawed. The entire experiment was based on only four people. Only the first subject actually lost 21 grams. Another person lost a different weight, and the other two died before they could be properly weighed.