The name says it all. The deadly nightshade is deadly and is one of the most poisonous plants in the world. This is due to the alkaloids found in its berries, roots, stems, and leaves. Not only is ingesting it poisonous, which may cause death if ten to twenty berries are ingested by an adult but even rubbing against it irritates the skin. If ingested, other symptoms include enlarged pupils, dry mouth, vomiting, stomach pain, diarrhea, slowed breathing, delirium, and paralysis (Best Life Online).