Factor by grouping x^3 + 8x^2 - 2x -16?

Usually, such a problem statement means we can group the first two terms and the last two terms
  x^3 + 8x^2 - 2x - 16
  = x^2(x+8) - 2(x+8)
  = (x^2-2)(x+8)
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If the constant 2 in the first factor were a square, then it could be further factored.