Freegans part 19

Cara
I didn't want to admit it, but my eyelids were growing heavy, and it was all I could do to keep from dozing off. But as the (rather self-appointed) leader, I had to try and keep a good profile. I was doing my best, but I could tell Matt wasn't fooled.
"You should go to sleep, Cara. I can take the first watch," he said aloud.
"Don't be silly. I'm fine," I said indignantly, pinching myself quickly. Matt gave me a skeptical glance.
"Cara, you are tired. If you don't go to sleep this instant, I will make you."
"How?"
"By physical force, if necessary."

I glared at him, and then betrayed myself by yawning. Matt grinned triumphantly. "Fine," I muttered. Lucy and Ben were already down and out, and Madiza was just sitting by herself, muttering and drawing using one of the pieces of chalk that had been in the pack. I barely stopped to wonder what she was drawing before I was asleep too.
My dreams were mainly nightmares. I was chased by a giant, fanged helicopter, which kept trying to stab me in the back with its blades. No matter how fast I ran, the helicopter was always right on my tail. Then I stumbled, and was falling, into a giant mouth. The mouth began closing. I screamed in pain as one of the fangs stabbed me in the ribs.

I awoke with a start, and realized that Matt was poking me. "Whassup?" I mumbled, sitting up.
"Cara, I think you should see what Madiza's doing," he said. Giving me a hand up, he pulled me over. Madiza's chalk had been halfway used up by now, and what its purpose had been surprised me. She appeared to have drawn first the cross-section of an eyeball, with all the parts labeled and everything. Then she had scrawled some kind of complicated calculus equation, followed by a couple more mathematical formulas. Now she was writing a set of instructions for something. I read it quietly.
"To put together your computer, insert-" I stopped. Madiza had frozen, and was looking down one of the corridors. If she had been a dog, her ears would have been pricked.

"Madiza, what is it?" asked Matt. Madiza only cackled softly, before saying in a singsong tone, "Mr. B, Mr. B, Big Sister doesn't like you playing with me!" She snickered. I grabbed her shoulder and looked straight into her glassy eyes. "What are you talking about, Madiza?!" She didn't have to answer. Suddenly we all could hear a loud, creaking noise, heading straight for us.