One of the most important parts of writing a story that's truly scary is setting the scene. In order to induce chills and make people furtively check their sixes, you have to make them feel like they're in the story—and you do that by being very descriptive. Yancey has just about perfected the ability to make his readers feel like they're in the room with the characters:
The shoe broke apart in the doctor's hands as it pulled free. The stink of decomposing flesh washed over us in an unwonted, nauseating wave. When the boot came off, the skin encased within came with it, sloughing off in a single, curdled mass, and thick, viscous pus the color of pond scum gushed onto the sheets. (6.258)
Okay, so gross. But see what we mean? This brief description has everything we need to feel like we're right there with Will Henry—and to deeply appreciate that we actually aren't.
The tool of alliteration can be used in many ways, but Yancey uses it mainly to create rhythm and provide a little extra emphasis on the point he's trying to make. For example:
I stripped out of my clothes and crawled beneath the covers, but the hours of sleep I snatched were scant, and teemed with vivid visions of voracious vermin: worms and maggots and the sightless, nameless, colorless creatures that dwell in the dark beneath rocks and wet, rotting logs. (8.1)
Yancey starts off with three hard c's ("clothes," "crawled," and "covers") that are pretty evenly spaced, which has the effect of creating a beat. Try saying it out loud and nodding your head with the c's… isn't it the same motion you do when enjoying some particularly good music?
Then Yancey moves onto s's with "hours," "sleep," "snatched," and "scant," which creates what us literary types like to call sibilance, which is basically alliteration that creates a hissing sound. Many times this literary device is employed to create a tense, sinister, sensation—gee, why would Yancey want to do that?
And then he hits the hard stuff, punching the v's with "vivid visions of voracious vermin." Once again, if you read the sentence out loud (which is really the best way to catch any alliteration), you have to almost snarl to get all those hard consonants out. This helps emphasize the nastiness that he's describing.