Irkens compete in gladiatorial-style blood-sport matches, similar to the gladiators and warriors of ancient Rome. For example, in a cut scene from "The Nightmare Begins", Zim was forced to combat the Digestor, an arena beast, whilst wearing the armor typically worn by Irkens in these fighting tournaments. When a Tallest is killed or incapacitated, the Control Brains will choose the next tallest Irken to take his, her or their place.