JOHNNY: I'm gonna give you to the count of ten to get your ugly, yellow, no good keister off my property before I pump your guts full of lead!
SNAKES: All right, Johnny, I'm sorry. I'm going.
JOHNNY: 1, 2, 10! [Shoots Snakes.] Keep the change, ya filthy animal.
This is from the violent movie—Angels with Filthy Souls—that Kevin's Uncle Frank wouldn't let him watch. Initially, it freaks Kevin out, but he later uses it to spook the pizza boy and the two burglars. He gets over his own fear, allowing him to inflict fear on others.
HARRY: Why the hell did you take your shoes off?
MARV: Why the hell are you dressed like a chicken?
In the midst of their encounter with Kevin's booby traps, both Harry and Marv are bearing marks of physical trauma. Watching these two grown men get systematically dismantled, we realize: Kevin is straight-up ruthless.
KEVIN: You guys give up or are you thirsty for more?
Kevin is actually enjoying the process of beating the tar out of Harry and Marv. He's discovered his inner hero—and that inner hero looks a lot like a terrifying Viking warlord.
HARRY: You bomb me with one more can, kid, and I'll snap off your cajones and boil them in motor oil!
The burglars can only make threats—they've been rendered incapable of fulfilling them, thanks to Kevin's cleverness (though they almost get Kevin in the end).
MARV: I'm not going out the window!
HARRY: What're you scared, Marv? Are you afraid? C'mon, get out here!
Even though Harry's supposed to be the smart one, he's been so disconcerted and injured by these booby traps that he's making a rash and totally stupid decision. Kevin, of course, cuts the line they try to use to climb to the tree house.
MARV: What are we gonna do to him, Harry?
HARRY: We'll do exactly what he did to us: we're gonna burn his head with a blowtorch!
MARV: And smash his face with an iron!
HARRY: How about slap him in the face with a paint can!
MARV: Or shove a nail through his foot.
HARRY: First thing I'm gonna do is bite off every one of these little fingers, one at a time.
Fortunately, Harry doesn't get a chance to bite Kevin's fingers off—Marley shows up and smashes Harry and Marv over the head with his snow shovel. But would Harry have actually bitten those fingers off, though? Probably. Kevin did just torture them.