"Probably not. I don't know of any way to be sick that involves having no heartbeat and being otherwise fine."
"That's a very good question and I wish I knew how to answer it."
"Short version," says Chris, "when people breathe, we get oxygen from the air, which is something our bodies need to have all over the place in order to keep working, and we have blood to take the oxygen from the lungs all the way around to everywhere else, and the heart is the thing that pumps the blood to keep it going around, and the thumping is the sound it makes when it does that."
"I looked up blood in the dictionary. It wasn't very helpful."
"It said it was a fluid in animals that does - things, but we aren't animals, are we?"
"Some people don't like to think so, but we are the kinds of creatures that have blood. At least," she looks at Katie contemplatively, "the rest of us are. I'm getting less sure about you."
"There's ways," says Chris. "I'd consider these a sign." She shows Katie the blue veins on the insides of her wrists. "They are veins. They contain blood. It's red when it has oxygen in it, blue when it doesn't. Let's have a look at your arms and see if we can find any."
They are the same color all over. There are no raised lines for blood to travel through.
"No veins," she concludes. "But they could still be there; I don't think everybody's veins are the same amount of visible. Other ways to tell... well, under normal conditions people's blood stays inside of them, but if something pokes a hole in our skin, we leak."
"Nope. Tiny ones work just fine. Better, actually, because if we leak too much that is generally considered very bad for us."
"I want to know if I have blood. The hole goes away later? Right?"
"On people with blood, it does. Usually pretty fast, if it's a small one."
"What about if you make holes in other kinds of alive things, though?"
"In any kind I can think of, the hole goes away. Maybe not as fast in some cases. And some kinds of alive things are too small to poke holes in very easily, so I wouldn't know about those."
"Yes..." says Chris. "I can. But I think I'd rather not do it now. There are things specially designed for safely poking small holes in people to get a little bit of blood, and I don't have any in the house, but I can get some."