Some mushrooms are poisonous only if eaten with alcoholic beverages. Some mushrooms are classified as poisonous because they are hallucinogenic. Some mushrooms that are edible when fresh and young become poisonous when they are old, hit by frost or if they decay. Some mushrooms, for unknown reasons, are poisonous in one part of the country and are not poisonous in another. Some mushrooms that are poisonous to animals do not cause major problems in humans.
Most mushrooms are more dangerous to young children, the aged and the very ill.
Ideally, people and animals should never eat mushrooms that have not been identified by an expert or bought at the store. Unfortunately, many mushrooms are difficult to identify even for a trained mycologist, a biologist trained in the study of mushrooms. Identifying mushrooms is an exact art that is very difficult and time-consuming. Before making a positive identification, mycologists look closely at the color, gills, spores, stalks and base portion of the mushroom. Spores are examined under a microscope to detect differences.