Thousands of plants around the world contain varying amounts of poison, or those properties that can injure animals or people. Plants may be poisonous to the touch (such as poison ivy and poison sumac) or toxic if swallowed (such as deadly amanita or poison hemlock). Sometimes the entire plant is poisonous, and other times a certain part of the plant such as the seeds, leaves, berries, and flowers is poisonous. For example, the leaf blades of rhubarb are poisonous, but not the stalks. Many times, there is not enough poison to affect humans, and sometimes cooking the plant destroys its poisonous substance. Some plants have substances that are dangerous to some animals, but not others. For example, onions occasionally poison horses or cattle, but are widely used for human food. Poison ivy or poison oak can affect some people’s skin, but not others, and goats eat it regularly without any side effects. Some of the more common poisonous plants found in the United States and Canada are belladonna, daffodil, foxglove, holly, iris, lily-of-the-valley, mistletoe, morning glory, and rhubarb.