Spotting the gills in a cross-section can be less clear than in that shared pict...

Spotting the gills in a cross-section can be less clear than in that shared picture, as well - here are a few more subtle examples:

Which is not to say never go mushroom-hunting; I and many thousands of other people forage regularly without dying, but the very most important thing is to know what all the deadly mushrooms in your area look like and be able to rule out them out anytime you plan to eat a foraged mushroom.