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The obvious question here is whether the grandparents were being generous and ignorant or devious and evil. My money's on devious, of course. Not only do they know they're going to be noisy with those instruments all through the house, I bet they also didn't bother to pay for lessons either. They want it to be as noisy and horrible sounding in the house as possible, to get back at Elly for whatever terrible thing she did to them in some previous year. That look on her face tells me she remembers it, too, and is thinking, "I guess this is what I deserve."