You want to think about something else? Here:
Is it possible for two entirely material things... to be made of the same matter at the same time? Pah, you might think, but not so fast.
Consider the ordinary human being Robert. There is such a thing as Robert's left hand. If there is, there is also such a thing as his 'left-hand complement', something composed of Robert's particles save those which make up his left hand. Call that 'Bob'. Robert and Bob are not the same things - for a start, Robert is a little bigger. Suppose Robert's left hand is amputated. Robert can survive this, but what about Bob? If the cut is seriously clean, Bob is not affected at all. Robert and Bob then coincide - there are two things made out of the same matter at the same time.
I don't know; either I'm missing something, or James Garvey is ambiguous about what the referent of 'Robert' is. If Robert is supposed to be the material thing that is Robert's body when he still has a left hand, then after the cut Robert is no more. There is just Bob, i.e. Robert minus that left hand, and therefore no Robert in the sense of the integral two-handed body that Robert used to be. On the other hand, if Robert is 'the ordinary human being Robert', then his name is being used in the sense of the person with the identity Robert. This Robert can indeed lose his left hand and still remain who he is. But this Robert isn't then equivalent to the full-bodied Robert with the two hands before the fateful cut. And he isn't identical with Bob now that he (Robert) has only one hand. If he lost the other hand - and an eye - he'd still be Robert, whereas Bob would not still be Bob.