Complex sentence: To penetrate the nut's hard protective shell, a metal vise or hammer can be used to compress the shell until it lightly fractures, then the pressure is released and the nut is repositioned to crack it along a different plane.
Split into simpler sentences: To penetrate the nut's hard protective shell, a metal vise or hammer can be used. Compress the shell until it lightly fractures, then release the pressure and reposition the nut to crack it along a different plane.