In the center of each [palm] was an eye inked in deepest indigo, in effect turning [Karou's] hands into hamsas, those ancient symbols of warding against the evil eye. (2.70)
The hamsa has roots in Jewish mysticism. What do the real hamsas have in common with the fictional Karou's hamsas?
If you opened [the door] from without, it revealed only a mildewed laundry room. [But] when the door was opened from within, it had the potential to lead someplace quite different. (5.7)
The idea that a door might lead to somewhere different is a magical idea that unlocks a lot of imagination. Remember the Chronicles of Narnia? Or Beetlejuice?
Around the world, over a space of days, black handprints appeared on many doors, each scorched deep into wood or metal. (7.1)
Why do you think the angels chose a black handprint as their threatening symbol instead of some graffiti, like "UR GONNA DIE"? Perhaps their handprints have something to do with the hamsas, another hand symbol. Maybe the hamsas and the black handprints are two sides of the same coin: the hamsas course with righteous energy, but these black handprints seem evil.
"Scuppy shing lucknow gavriel bruxis!" (21.10)
Not only does Karou finally explain the hierarchy of power when it comes to wish coins here, but she does it in order. Where do think the names of these coins came from?
Kaz [...] perceived that his ex-girlfriend was in midair. (28.2)
And he's pretty much like, "whatever." All of Karou's supernatural weirdness, no matter how much she tried to hide it, desensitized Kaz a bit over the months. So flying just isn't that big of a deal to him. Also, he's kind of a jerk, so.
"There was magic coming through the doorways. Dark magic." "From here? There's no magic here." "Says the flying girl." (30.63)
Here, Karou is called out for being kind of blind to supernatural goings on, since she is living them all the time. Also, to Akiva, Karou's world is a little supernatural as well. And now there's Brimstone's dark magic, but we still don't know much about it at this point.
[Karou] went out onto the balcony instead, climbed up onto the balustrade, glanced back over her shoulder at Akiva, and stepped right off. (31.20)
Karou has gotten so used to her supernatural existence, she steps off a balcony like she does it every day... even though she's only been flying for about twelve hours. This act shows that she has a lot of faith in wish magic. Boy, if it didn't work, that would be a crazy way to end the book, huh?
"We didn't break any laws. [...] It's not like there's a law against flying." "Yes there is. The law of gravity." (33.56)
Here's another bit of evidence that Karou has embraced her supernatural lifestyle. We flew, so what? She doesn't even consider that us terrestrial human folk might think that this is a little weird. If she flew around over L.A., she'd have her own reality TV show by now. Criss Angel, eat your heart out.
Brimstone was a resurrectionist. He didn't breath life back into the torn bodies of the battle-slain; he made bodies. (49.8)
We knew Brimstone was a supernatural being before this point—he has crocodile eyes and ram horns, after all. But now we finally found out what he's been up to all this time. The chimaera aren't inherently supernatural, when you think about it. They're just a different race of half-animal people. But this resurrection thing makes them supernatural.
[Madrigal] learned that magic was ugly—a hard bargain with the universe, a calculus of pain. (49.38)
Magic isn't all fun and games, the way Karou has always made it out to be. Why didn't Brimstone tell her this sooner? He always hinted that she shouldn't make frivolous wishes, but he never told her the price was another's pain. Jeez.