Percy made a valiant attempt to laugh, failed utterly, and set to work. Ron, thankfully, was entirely silent as Percy muttered to himself, drawing imaginary charts in the air with his fingers and pointing from one bottle to the other. This was not the sort of thing he did for fun, but it was the sort of thing he was good at, since it involved basic deductive reasoning and, like Arithmancy, did not require you to make arguments for your facts; they were either true or they weren't.