The character Nora was originally described as having brown skin and being half Ethiopian, but they instead decided to go with a Caucasian actress (Analeigh TiptonAnaleigh Tipton).
The actors portraying the zombies in this film chose not to blink. It was particularly uncomfortable for Nicholas HoultNicholas Hoult who did a few long scenes without blinking. Later in the film (when the zombies become more human), the zombies start blinking.
When R is talking to Julie outside her house the scene is referencing to the balcony scene of "Romeo and Juliet". R (Romeo) is talking to Julie (Juliet) on the balcony.
The story is based loosely on "Romeo and Juliet". "R" = "Romeo"; "Julie" = "Juliet; "Perry" = "Paris"; "M/Marcus" = "Mercutio"; "Nora" = Juliet's "Nurse" (the character of Nora is also a nurse).