Actress Jenna Fischer disclosed on a TV talk show that she got the role of Shelby as a "birthday present" from her spouse, director James Gunn, after another actress dropped out of the movie. Being a big fan of zombie films, she always wanted to play a zombie; upon hearing the news, she screamed with joy.
Haig Sutherland was the first person to be cast. Elizabeth Banks was the second. Gregg Henry was the last actor to be seen for the part (out of more than 100 actors from Los Angeles and Vancouver) and nailed his audition. Nathan Fillion was the last actor to be cast, about a week before shooting began. Shooting lasted 47 days.
Dangled above the street at the beginning of the film and on stage later at the Deer Cheer celebration you can see "Henenlotter's Saddle Lodge presents Deer Cheer" signage, a clear reference to cult horror writer/director Frank Henenlotter, famed creator of Basket Case (1982) and Brain Damage (1988).
(at around 48 mins) When the mother tells her two daughters to go to bed, the one on camera right is reading a "Goosebumps" story by children's horror author R.L. Stine entitled: "The Girl Who Cried Monster." This series was popular from the early to late 1990s, and is still well known in the early twenty first century.
The trivia item below may give away important plot points.
The post-credits coda shows a cat getting possessed by the last surviving creature. In an early draft, this was meant to happen to Bill, after the Grant-creature is destroyed. Starla sees the resulting wound later, prompting her to shoot Bill to death.