A great way to safely examine mushroom gills is to buy some portobello mushrooms from your grocery store. This allows you to pick and prod at them to your heart's content. You may see some recipes asking to remove the gills before cooking. This is not due to any danger but for aesthetic reasons. The gills tend to give a darker, grayish color to the rest of the meal, which may not look very appetizing! - See more at: http://www.mushroom-appreciation.com/identify-mushrooms.html#gills