This episode introduced the Andorian and Tellarite species. John Wheeler, the actor who played the Tellarite ambassador, Gav, had difficulty seeing through the eye holes in his prosthetic makeup and was forced to raise his head in a seemingly arrogant manner in order to see the other actors. The Andorian antennae (sprouting out of the back of the head in this and other episodes of the original series) were depicted in the later "" series as coming out of the forehead and capable of movement.