(at around 55 mins) After devouring a security guard's brain, a zombie picks up a phone the guard had been speaking into and says "Send more security guards!" This pays direct homage to the original The Return of the Living Dead (1985), in which a zombie who had been devouring a paramedic picks up the radio in the ambulance and says "Send more paramedics."
Both this film and the next entry Return of the Living Dead: Rave to the Grave (2005) stray away from the series' rules that the Trioxin zombies are no longer the indestructible juggernauts of the first three movies, but instead much weaker and sometimes are seen to be dispatched with no more than a few body gun shots. Prior to this film, nothing short of incineration or electrocution with extreme high voltage would destroy a Trioxin zombie.
Director Tobe Hooper was once attached to direct this and Return of the Living Dead: Rave to the Grave (2005) early in pre-production.
The chemical that brought the dead back to life in the previous Return of the Living Dead films was 2-4-5 Tioxin. In this film the chemical is referred to as Trioxin 5.