It often seems as though each modern horror movie can at least muster up one virtuoso sequence, something better than the sum of its parts. Alexandre Aja’s Mirrors is often staid and unremarkable, but there’s a moment in there where Amy Smart’s character performs an act of self-mutilation stunning in its gory, go-for-broke visual flair; we can even go back to 2002’s three-alarm snoozer Ghost Ship, which opened with a stunningly gross prologue that belongs in the horror kills hall of fame.

It’s true that to love horror movies means to embrace them warts and all — unfortunately, sometimes those warts hinder movies from becoming stone-cold classics. Still, that doesn’t mean that their best moments aren’t terrific; as with any art form, film varies in consistency. Today, we’re veering away from the classics and looking at a pair of movies that contain brilliantly scary scenes, but falter as fully-formed films.

The much vaunted “killer terrorizes babysitter over the phone” opening of When a Stranger Calls is justly heralded as a classic moment in horror cinema. It’s an old urban legend, the kind of thing people tell over candlelight on foggy nights, but a potent one; the punchline, as a 911 dispatcher traces the eerie phone call to an upstairs line in the same house, hits the gut hard with primal terror. And the 20-minute prologue of When a Stranger Calls crystallizes this fear perfectly; the mysterious calls are creepy and deeply unsettling, and there’s some killer play with shadows and tension near the end. It ebbs and flows like a legitimate film in its own right, which is far from a coincidence; after the success of John Carpenter’s landmark slasher Halloween in 1978, director Fred Walton decided to flesh out his short film “The Sitter” — which was basically comprised of, you guessed it, simply the extended prologue — and turn it into a feature-length slasher.

Unfortunately, When a Stranger Calls doesn’t work at feature length. The killer, as played by the late Tony Beckley, has his creepy moments — it’s a wonderful performance on Beckley’s part, foreshadowing Joe Spinell’s lusty creeper one year later in Maniac! — but the film itself flows like a humdrum police procedural. It’s as if Halloween gave up the ghost halfway through and turned into Serpico, except Stranger turns 20 minutes earlier than the halfway point, and the procedural it becomes isn’t half as engrossing as Serpico. But it’s difficult to live up to the promise of Stranger‘s opener, a perfect 20 minutes of horror cinema, injected with pure, unfiltered dread.

Less known is director John Simpson’s direct-to-DVD Amusement. Compared to Stranger, however, it actually manages to stay potent for longer. It bears the structure of an anthology, with three individual plot threads dovetailing into one unified climax — and spoiler alert, the second half of the movie is pure, unfettered crap. With the mysterious villain’s face obscured and motives unclear, Amusement is legitimately terrifying; when all becomes clear, and the killer is unveiled as a cackling jackass with a ridiculous childhood grudge, the movie falls to pieces quickly.

That doesn’t mean that it doesn’t deserve some measure of praise, though. Simpson cunningly devotes each vignette to a different staple of horror, and Amusement‘s nicely-done opener brings to mind the highway horror of Joy Ride and Duel. It’s a promising installment, but nothing compares to Amusement‘s stellar centerpiece: once again, we encounter a babysitter in someone else’s house, whose night quickly goes awry when the ominous life-sized clown mannequin at the foot of her bed starts to move.

Let me be frank: it’s terrifying. And not in that cheesy, “let’s capitalize on fear of clowns” way — it’s terrifying down to the very soul to see this thing, previously thought to be an inanimate object, turn its head. It’s even scarier when it becomes clear that this “mannequin” is actually a madman unusually good at sitting still. It’s difficult to explain how this little vignette, nestled in the middle of such a scattershot, hit-or-miss flick, manages to elicit a stifling sense of terror; it’s a scene straight out of a better movie, and it deserves to be recognized as such.

So, no: When a Stranger Calls and Amusement are not great films. But both contain moments so breathlessly terrifying that they demand to be seen, especially by any self-respecting horror movie fan. You can stop the movies whenever, really — nobody cares about the boring old horror-by-numbers flicks they both eventually turn into — but these films have moments where they are deeply and thrillingly “on”. You wouldn’t avoid a great song because the album was kinda lame, right?

More 31 Days of Halloween:
Day 1: May
Day 2: The Night of the Hunter
Day 3: The Descent
Day 4: Night of the Demons
Day 5: Them
Days 6 & 7: Night of the Living Dead // Dawn of the Dead
Day 8: Behind the Mask: The Rise of Leslie Vernon
Day 9: A Tale of Two Sisters