George Romero, who pioneered the modern zombie film in 1968, complained in 2010 that he’d “never had a zombie eat a brain, but it’s become this landmark thing.” The trope was introduced in 1985 by Dan O’Bannon’s Return of the Living Dead, in which a zombie woman explains that eating brains relieves the “pain of being dead.” Some fans have speculated this is due to the brain’s high levels of serotonin.