Nightmare Fuel: The closest things we get to scares are the fact we don't see what the lizard DOES to its victims (bit of a letdown, but judging by the screams in the train, it wasn't pretty) and the trailer. Said trailer makes good use of its music and signature line: "You're driving a lonely road...You're as good as dead...".
Purity Sue: Chase Winstead. Devoted son and older brother, reliable breadwinner (Dad being dead and all), and the resident Big Man on Campus who nevertheless tries to be be a responsible influence on his younger friends. His petty theft of wrecked car parts for his own ride is pretty much the only imperfection about him, and even that gets glossed over.
Special Effects Failure: The props occupying the sets that the lizard (which was a real Gila monster) crawls on are pretty obviously miniature models. It also turns out it's not even a real Gila Monster, but a Mexican Beaded Lizard. They couldn't even get the species right.