Red has historically been connected with blood, which is linked to bravery, sacrifice, revolution, and agony. Because of its association with pain, red elicits a sense of anxiety and awareness, making it an appropriate hue for danger or warning. The connection between blood and danger applies not only to the color red but also to the substances red wine and red meat. Alcohol contains the chemical anthocyanidins, which are responsible for coloring grapes and other fruits and vegetables blue, black, or purple. The same chemicals that give strawberries, cherries, and plums their bright colors also make them poisonous if ingested. The human body cannot digest meat that is still bleeding, so it can pass into the digestive system and cause problems there. In medicine, red signals that something is wrong and that patients should be careful or not do things like eat spicy foods or drink alcohol. A medical emergency sign using red tape is used to warn people that help is on the way or that someone needs attention from a doctor. The connection between blood and danger extends beyond fruit, vegetables, and meat to objects in the real world as well. There are many items that are naturally red, such as rubies, garnets, and coals, that have no relation to blood at all but that people have associated with danger because of their appearance.