Eggshell membrane is derived commercially from the eggshells of industrial egg processors. These include beer traps, diatomaceous earth, crushed eggshells, coffee grounds, and copper. Hunter-gatherers in the Kalahari use ostrich eggshells as water containers, punching a hole in them. Hatchlings may stay inside their eggshells after hatching for the first day or two. Shortly after hatching, she removes the empty eggshells from the nest. Newly emerged larvae eat their own eggshells before feeding on fresh foliage. Other bird species will use porphyrins to pigment eggshells in the oviduct. This is consistent with the eggshells surrounding the embryos of viviparous reptiles being non-calcified membranes. Gas exchange across eggshells results in water loss from the egg. It also includes organic matter such as eggshells, bone chips, seeds, and coffee grounds. Ground eggshells sometimes are used as a food additive to deliver calcium. The eggshells of brood parasites are often thicker than those of the hosts. Later, her pupal case can be found, full of the yellow remains of eggshells. Empty eggshells (known as nits) are not sufficient for the diagnosis. The family walked on eggshells and "Bob" de Man found solace with other women.