A jackrabbit was an Earth mammal closely related to the rabbit. When James T. Kirk discovered, in 2267, that violent emotions were the means required to destroy the Omicron spores that had taken over his crew, he was forced to make several insulting remarks to his first officer Spock in order to break him free of the spores' influence. Into the confrontation, Spock claimed to be a man, not a computer, to which Kirk replied, making obvious analogies to Spock's ears, "What makes you think you're a man? You're an overgrown jackrabbit, an elf with a hyperactive thyroid." (TOS: "This Side of Paradise" )