Fart lighting, also known as pyroflatulence or flatus ignition, is the practice of igniting the gases produced by human flatulence, often producing a flame of a blue hue, hence the act being known colloquially as a "blue angel", "blue dart", or in Australia, a "blue flame". The fact that flatus is flammable, and the actual combustion of it through this practice, gives rise to much humorous derivation. Other colors of flame such as orange and yellow are possible with the color dependent on the mixture of gases formed in the colon. In order to "fire fart", one must have a fart prepared in the anal cavity, and a lighter at the ready. Then they fart onto the lighter.