“You should climb around inside my brain, Dan. It's like this dark room surrounded by quicksand.""I know what you mean," her brother said quietly. "I hate being in my brain sometimes. I have to get out.""What do you do?" Amy asked.Dan shrugged "I go to other places. My toes. My shoulders. But mostly here." He tapped his chest and immediately reddened. "I know. It's stupid.""Not really," Amy said. "I wish I could do that, too.”

“No, I'm not a jerk, Astrid. You know what I am? I'm the guy getting people killed," Sam said quietly. Then, "My head is exploding from it. I can't get my brain around it. I can't do this. I can't be that guy, Astrid, I'm a kid...”

“It's such a stupid question, in my opinion. I mean, how do you know what you're going to do till you do it? The answer is, you don't. I think I am, but how do I know? I swear it's a stupid question.”

“I've never really apologised to her for that specifically, mostly because I didn't know how to apologise for my brain not working.I can't see girls being cool with... "Hey, sorry about my brain not working right; that things is nuts sometimes. I know I might have confused you, but my brain confused me too. Anyhoo...just letting you know that was why! Hugs!"I mean, I'd be willing to try it once...but just for the story, really.”

“Who knows what I want to do? Who knows what anyone wants to do? How can you be sure about something like that? Isn't it all a question of brain chemistry, signals going back and forth, electrical energy in the cortex? How do you know whether something is really what you want to do or just some kind of nerve impulse in the brain? Some minor little activity takes place somewhere in this unimportant place in one of the brain hemispheres and suddenly I want to go to Montana or I don't want to go to Montana. How do I know I really want to go and it isn't just some neurons firing or something? Maybe it's just an accidental flash in the medulla and suddenly there I am in Montana and I find out I really didn't want to go there in the first place. I can't control what happens in my brain, so how can I be sure what I want to do ten seconds from now, much less Montana next summer? It's all this activity in the brain and you don't know what's you as a person and what's some neuron that just happens to fire or just happens to misfire.”

“I've got a few ideas," (Amy) admitted. "But I don't know where we're going in the long term. I mean - have you ever thought about what this ultimate treasure could be?""Something cool." (Dan)"Oh, that's real helpful. I mean, what could make somebody the most powerful Cahill in history? And why thirty-nine clues?"Dan shrugged. "Thirty-nine is a sweet number. It's thirteen times three. It's also the sum of five prime numbers in a row - 3,5,7,11,13. And if you add the first three powers of three, 3 to the first, 3 to the second, and s to the third, you get thirty-nine."Amy stared at him. "How did you know that?""What do you mean? It's obvious.”