Ready for a mouthful? The Everpresent Wordsnatcher, the Terrible Trivium, the Demon of Insincerity, the Giant, and the Senses Taker. These are five of the scariest demons that Milo, Tock, and the Humbug encounter as they pass through the Mountains of Ignorance on their way to the Castle in the Air.
First on the list is the Everpresent Wordsnatcher. He turns out to be not that bad compared to the rest: it's just impossible to hold a conversation with him! Frustrating, yes. Life-threatening, not so much.
The other demons are a bit more complicated. Milo ends up using all four gifts given to him by King Azaz, Alec Bing, the Soundkeeper, and the Mathemagician to defeat these terrible creatures.
First, the Terrible Trivium forces Milo to use his gift from the Mathemagician, the magic staff. See, the Trivium looks like a "very pleasant man" (16.116), but he has a blank face. That should be the first clue that he's a lot more trouble than he appears. He gives Milo, Tock, and the Humbug tasks that seem urgent but are really just tedious (picky). Milo's only able to figure this out by doing some math (using the handy pencil/staff).
The Trivium becomes even more frightening when he's found out. His blank face ends up becoming super-scary when he explains how he has trapped the travelers into doing meaningless tasks: "his face looked as if he'd be grinning an evil grin – if he could grin at all" (17.20). It's a good thing Milo, Tock, and the Humbug can outrun him once they start to get away.
Next up is the Demon of Insincerity, who has a great voice but insignificant body. He uses his voice to trap Milo, Tock, and the Humbug in a pit where they can only hear him (and fear him!). That is, until Milo uses Alec's telescope to see the demon as he really is. Being seen makes the little demon fold like a pack of cards:
"I don't mean what I say, I don't mean what I do, and I don't mean what I am. Most people who believe what I tell them go the wrong way, and stay there, but you and your awful telescope have spoiled everything. I'm going home." And, crying hysterically, he stamped off in a huff. (17.43)
Once he's gone, the travelers can climb out of the pit. But, of course, they walk right into the hand of a giant. This big guy wants to eat our heroes, he can't stand new ideas because they make him sick to his stomach. (Perhaps, allegorically, he's supposed to represent towering intellectual figures who are stuck in their ways and don't want to hear anything new. Sounds about right to us.) Milo uses the box of words from King Azaz to defeat the giant, who doesn't even need to see the ideas to feel sick. Just the thought of them is enough.
Finally, the travelers have to defeat the Senses Taker. The Senses Taker seems like an unassuming little man who merely wants to get information from them. But he keeps asking and asking questions until Milo, Tock, and the Humbug have told him all they can. Then, he literally takes their senses! He distracts them with fantasies, which trap them in place so the other demons can run up and get them. Luckily, Milo has one gift left: the Soundkeeper's collection of sounds. When he drops them (totally by accident!) they all hear laughter, the one thing that can defeat the Senses Taker. Whew.
The demons are all scary in different ways and they each warn us against certain types of behavior: like, say, spending time on worthless activities, pretending to me more than you are… you get the idea. But by the time he gets into the Castle in the Air, Milo has been able to defeat each and every one of them using the knowledge he gained so far in Wisdom. Learning sure is coming in handy.