When the zombies are eating the bodies in the burnt-out truck they were actually eating roast ham covered in chocolate sauce. The filmmakers joked that it was so nausea inducing that it was almost a waste of time putting the makeup on the zombies as they ended up looking pale and sick anyway.
From IMDB: Trivia
I’m going to get to see George A. Romero at the Rue Morgue Dark Carnival in July! Night of the Living Dead was one of the first horror movies that made me fall in love with the horror genre. The movie’s political commentary elevated the horror to surrealism, and I’ve yet to see that done as well again.
Romero, George A. Night of the Living Dead, The Walter Reade Organization / Continental Distributing, 1968.