This furnace makes the talking appliances from The Brave Little Toaster look like mere child's play.

When Kevin goes into his basement, the house's furnace metamorphoses into a talking, grumbling demonic presence that threatens and mocks him.

FURNACE: Ha ha ha! Hello Kevin! Ha ha ha!"

It's not an especially articulate furnace, but it is scary: gnashing its grill like it's about to devour him.

Of course, this is all in his imagination.

Kevin bolts out of the basement the first time, but later on, he puts on his big boy pants (metaphorically speaking) and defies the furnace, saying "Shut up!" In response, the furnace…shuts up.

Kevin: 1. Imaginary Furnace Monster: 0.

The furnace is a pretty obvious metaphor for Kevin's fears. At the beginning of the movie, he's too afraid and timidly incompetent to do basic household tasks, and backs away from Old Man Marley because he believes Buzz's lie about Marley being a serial killer.

But, as the movie progresses, Kevin confronts his fears and banishes them. After he gets the furnace out of his head, we see him shopping for food, chatting with Marley at church, and, oh yeah, putting two robbers through a grueling Saw-like maze of horror and pain.

(The Saw reference cannot pass without citing this article, which supposes that Kevin grew up and become Jigsaw. Brr.)

Growing up and becoming an adult isn't just a matter of shopping for eggs and fabric softener—although Kevin succeeds at that too. It's also a matter of smiting your enemies with wrath and furious anger, preserving your house and fortune. But in order to do either of these tasks, you need to confront and defeat the enemy within.

And that's where Kevin's furnace monster really is after all—it's in his mind, not in his basement.