According to Lawler, a rough version of the song was initially titled "In Your Head", which was included in the band's live set; it was then later revised to "Zombie".
First off, in the old movies, the word Zombie was snicker inducing. If you're trying to be serious, and someone on screen says Zombie, all pretense of seriousness is gone. Then and now, 'Zombi' is a funny sounding word to English speakers.