THERE ARE MANY SCIENTIFIC mysteries that are still waiting to be solved. For example, is light a wave or a particle? What causes gravity? Does alien life exist? How did the universe begin? And why is Ashley’s behavior so baffling?

One moment she acted like I was invisible; the next she was inviting me to sit down and have a cup of tea. She even got the mug herself, and put in lots of milk and sugar when I asked, because Red Velvet Cake tea is still tea.

“Sit,” she said, patting the cushion on the other end of the couch. So I sat. Schrödinger curled up in my lap. I try not to anthropomorphize animals, but I swear he eyed Ashley with suspicion.

“How do you know Jared?” she asked.

“We’re in phys ed together.”

“And how did you get to talking about me?”

“Well,” I began. I tried to figure out how much I should tell her. My mom always said that honesty is the best policy, but then again, she also told her share of white lies. Things like telling our neighbor Mrs. Janowski that, no, she didn’t notice she’d gained any weight, when, in fact, Mrs. Janowski had ballooned two dress sizes in six months. Or when she scratched the side of the car when we went shopping and told Dad, “Someone scratched the car in the parking lot.” It wasn’t a lie, exactly; she just didn’t tell him that the “someone” was her.

“It’s kind of a funny story,” I began. “See, I thought Jared was about to do something really mean to me, so—and I know you’re not going to like this part—I told him you were my sister because last week I’d heard him say you were hot—”

Ashley put her hand up for me to stop. I waited for her to launch into a tirade, something like I’m not your sister, you freakazoid. But, scientific mystery that she is, she surprised me. “Jared said I was hot?”

“Yes. So I thought he’d stop picking on me if I—”

“How, exactly, did he say it?”

The question stumped me. “I don’t know. He said, ‘Ashley Anderson is hot.’ ”

“But did he say it as kind of a throwaway comment, or did he say it kind of dreamily?”

I had no idea what she was talking about, so I picked one. “Dreamily?”

That seemed to be the right answer, because she grinned from ear to ear. “Did he say anything else about me?”

“Not that I remember. It was a week ago.”

“So why are you only telling me now?”

I felt so confused. “I don’t know. I didn’t know it was significant—”

“Okay, fine,” she interrupted. “Tell me about today.”

“Well, when he found out we lived together, he became really nice. And then he said, ‘Tell your sister Jared said hi.’ ”

Again, I waited for her to freak out at the word sister. But she didn’t. She just beamed. It dawned on me that this was the first time I’d seen her genuinely happy since we moved in.

“I guess I should leave you to your show,” I said, taking one last sip of my tea.

“You can stay and watch it with me if you want,” she replied.

Like I said: scientific mystery.

But I peeled off my socks and stayed.