Dzanga Bai is a vast natural clearing in the middle of the Congo rainforest and a mecca for forest elephants. The forest provides them with all the food they need, but the clearing provides a vital mineral that they lack in their diet and cannot get elsewhere. Volcanic rocks lie just under the surface and the salts they contain help to neutralise the poisons contained within the leaves and bark that the elephants eat. Generations of elephants have come here to prospect for these minerals and settle their stomachs. Blowing air down their trunks into the muddy pools, they churn up the mud at the bottom and take mouthfuls of the mineral-enriched waters. As soon as the youngsters have mastered their trunks, they're hooked. It may be that these mineral salts are vital for the elephants growth and fertility and as many as 3,000 elephants visit Dzanga Bai each year. They are so important, the elephants will try any tactic to control the best places at the bai, and can be seen violently and noisily pushing one another away from the mineral wells.