Did you wake up today with a craving for clay, or dirt? That’s called pica, an abnormal craving for substances other than typical food. If you went ahead and acted on your impulse, it's probably a good idea to head over to your doctor’s office. Research indicates that in most cases this craving is a result of a mineral or vitamin deficiency. This brings us to this week’s Today I Learned, as National Geographic Society grantee and ornithologist Luke Powell explains why macaws regularly munch on South American rain forest clay. Yummy! All animals (including humans) need salt to live. Animals that live in the Amazon rain forest face a curious predicament due to the way the Andes mountain range affects weather coming from the Pacific Ocean. This geography results in an extreme lack of salt in the Amazon and, consequentially, some unique behaviors and appetites.EDITOR: Laurence AlexanderSERIES PRODUCER: Chris Mattle