Why is salt so precious in the rainforest?

Salt in the rain forest isn't as easy to come by as it is on the plains.

"Herds of elephants go inside Kitum Cave at night to obtain minerals and salts. On the plains, it is easy for elephants to find salt in hardpans and dry water holes, but in the rain forest salt is a precious thing. The cave is large enough to hold as many as seventy elephants at a time. They spend the night inside the cave, dozing on their feet or mining the rock with their tusks. They pry and gouge rocks off the walls, and chew them to fragments between their teeth, and swallow the broken bits of rock."