In the original storyline there was a side element in which Francis and Zoey develop a relationship with one another. However, test audiences found their romance to be "distracting" from the main storyline and so it was ultimately cut from the final version.
The basement of the house in Blood Harvest: The Train Station has a lot of blood and body parts spread around and also a turned over lawnmower; a reference to Dead Alive (1992).
On the campaign Blood Harvest, right at the beginning of the level is a fire. If you look closely you can see that they were burning a lot of money instead of fire wood.
If you look closely enough at the pain pills, you can see that they are Target brand.
According to the audio commentary available in the game, the original working title was "Terror Strike".