It's never directly explained why loved ones come back from the dead as vicious and murderous; the novel suggests that demons are possessing the corpses.
Bloody gashes and lacerations, ghastly head/face wounds on victims and zombies. Characters suffer cannibalistic attacks, being hit by cars, burning to death.
Just a reference to a cat spaying as "getting his nuts cut."
The s-word, "hell," and SOB.
Car brand names. Of course, there's a Stephen King book tie-in, and the Ramones had a minor hit with the theme song.
Smoking and beer-drinking among adults.