I've seen it done with a pig. The theory of the wick effect is proven. In cases of claimed spontaneous human combustion, upon investigation there has always been a source of ignition. Never the less, total burning, where there isn't even ash is still a remarkable phenomenon. There are two forms of genuine spontaneous combustion in nature. One is St. Elmo's fire, which is sometimes seen on ships and is caused by a form of ball lightning. The other one is Wil 'o the Whisp. This is where marsh gas in ponds can rise to the surface and ignite.