K9 Mark I, II, III, and IV addressed whomever was directing them as "Master" or "Mistress" depending upon gender, and used the formal "affirmative" and "negative" rather than "yes" and "no". They were programmed to be both loyal and logical, with a penchant for taking orders literally, almost to a fault. Their striped collars mirrored the Fourth Doctor's trademark scarf. The Twelfth Doctor stated that he took his K9s to Garage 10 for annual service. (COMIC: The Ministry of Time)