Sometimes the animal was already dead when used for testing. In 2259 of the alternate reality, Doctor Leonard McCoy injected a sample of Khan Noonien Singh's Augment platelets into a dead tribble. Later, while despairing over Kirk's death, the tribble came back to life, prompting McCoy to give Kirk the same treatment, which ultimately led to the captain being revived. (Star Trek Into Darkness) Some lab animals were more sensitive than others. In 2269, James T. Kirk inquired on the status of USS Enterprise's sickbay's sensitive lab animals. (TAS: "The Terratin Incident")