The coconut is the other important element in their diet, and one of the main economic resources. When, at the start of the twentieth century, it was discovered that copra oil greatly reduced the cost of steel manufacture, these islands became extremely important places for European industry. This is one of the reasons for the rapid colonisation of the region. To obtain the oil, they dry the copra, or pith of the coconut in these ovens. Then, they grind and press it. By squeezing the pulp of the coconut, they also obtain the highly nutritious milk. They use it as a drink, and to cook the cassava, wrapped in banana leaves. The coconut palm is one of the most valuable trees for the inhabitants of Papua. Virtually every part of it is used. From the husk, they make ropes and fabrics, and with the inner shell, which is much harder, they make all types of utensils. After extracting the oil, the copra is used as cattle feed. The juice of the flowers is boiled to obtain sugar. They also eat the young shoots, which have very high energy value. From the bark they obtain resin, and with the leaves make baskets, hats and the roofs of their houses. Finally, the wood is used to make furniture and oars, and in construction. Another extremely useful plant in these latitudes is the banana tree. Apart from the fruit, which is present at most meals, the leaves are used to wrap foods to be cooked or fermented. Dried in the sun, they make skirts and costumes with them. They also serve as tablecloths and even as umbrellas. The canoe builders are very important in these communities They have the same social status as the carvers of yam houses. A man may not have a house, but if he does not have a boat he virtually does not exist for the community. Even the old men, though they can no longer sail, keep their canoes, riddled with woodworm, at the side of their houses. Their souls will travel in them when they die. They are a symbol of life, which mystically unites them with the sea and maintains them in contact with the world of the living. When they die, their canoes are abandoned far from the shore, so the currents will carry them out to sea, to the mermaids who will accompany their spirit on its final voyage to the realm of the gods. They believe their boats bear the traces of all the acts and deeds of this life. They are the summary of everything they have been and everything they have done. When the canoes reach their final destination, the gods can read them and decide the fate of their souls.