Percy answered every question Ron asked him, not seeming bothered in the least by doing this while he was writing essays or drawing puzzling diagrams that Ron suspected were Arithmancy. Occasionally, he even assented to take a break and play chess. So Ron, fascinated and feeling like he was learning more than he had in the last several weeks of class as he figured out the flaws in his first term's work, ignored Fred and George every time they tried to draw him into a game of Exploding Snap or toss-the-salamander. The twins were utterly baffled by this behavior, but after Percy hexed them a few dozen times they left their brothers alone.