The Food and Drug Administration is investigating dog food that tested positive for traces of a euthanasia drug. The findings may indicate that companies are using euthanized animals to make their dog food, a practice that is illegal. Federal law also states that the drug, pentobarbital, cannot appear in any food. Pentobarbital is used to euthanize animals and has also been used in doctor-assisted death as well as in carrying out the death penalty.