Several hundred million people today practice the ancient custom of chewing betel. In south Asia, where the habit is most prevalent, the signs are hard to miss. Placed inside the cheek and sucked for hours, a betel wad turns saliva bright red, and betel users' spit does likewise to sidewalks and streets. People typically chew betel as a quid consisting of nut pieces from an Areca catechu palm mixed with powdered lime (calcium hydroxide) and wrapped in the leaf of the pepper plant Piper betle. Betel is used primarily as a stimulant. Areca nuts contain alkaloids that induce euphoria and raise a person's heart rate and skin temperature. Some chewers say a cheekful of betel aids digestion.