Porcupines in search of salt sometimes live in human places , eating plywood cured with sodium nitrate , certain paints , and tool handles , footwear , clothes and other items that have been coated in salty sweat . Porcupines in search of salt sometimes encroach on human habitats , eating plywood cured with sodium nitrate , certain paints , tool handles , doors , tables , houses , footwear , clothes and other items that have been coated in salty sweat .