"Haven't I Seen Me Someplace Before?" begins with Roger's birthday party, Jeannie granting him one special wish as a present. Envious of Tony's upcoming mission, Roger inadvertently wishes he could trade places with Major Nelson and go himself, and it's now Tony's voice coming from Roger's mouth and vice versa. Mrs. Bellows runs into Major Nelson at Roger's apartment building, both not privy to what has happened, while the real Nelson frantically tries phoning his buddy to get him to take back the wish. Dr. Bellows himself runs into Major Nelson at Tony's house, waiting for 'Major Nelson' to return home because he doesn't have Roger's keys. He conducts an examination of 'Tony' at NASA, where the latter realizes at last what has transpired. It's interesting to see how Larry Hagman and Bill Daily try to portray one another, especially the walk.