2 Added clarification regarding location of magnets and iron pieces
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Perhaps heAndy had stuck two small magnets on either lower corner on the back of the poster and two small iron pieces glued to the wall that would hold the magnets in place and keep the pictureposter taut.

It would not be a big deal for himAndy to get two little magnets and two small iron pieces from the prison's machine shop.

Perhaps he had two small magnets on either lower corner and two small iron pieces that would hold the magnets in place and keep the picture taut.

It would not be a big deal for him to get two little magnets and two small iron pieces from the prison's machine shop.

Perhaps Andy had stuck two small magnets on either lower corner on the back of the poster and two small iron pieces glued to the wall that would hold the magnets in place and keep the poster taut.

It would not be a big deal for Andy to get two little magnets and two small iron pieces from the prison's machine shop.

1
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Perhaps he had two small magnets on either lower corner and two small iron pieces that would hold the magnets in place and keep the picture taut.

It would not be a big deal for him to get two little magnets and two small iron pieces from the prison's machine shop.