The whole concept of the film is to show zombies having sex with the young Zoey (The only female survivor in the video game, who was a college student), and all 3 male survivors (Bill, Louis, Francis) having sex with her.
It was terrible homemade porno. The smokers had extendo-dicks (didn't see that one coming), the boomers (called sploudgers for some reason) spray cum on you when you injure it. DON'T WATCH IT!!!!
It accually makes you loose a boner
Zoey - Holy shit, a sploudger!!!! (stabs sploudger)
Sploudger - I will now spray you with zombie cum!!!