Pica is having an appetite for substances like clay, chalk, animal feces, dirt, hairballs, paint. which might have lead, and sand. Eating this way must occur for at least a month to be considered pica. It is very dangerous, but it is not uncommon in some cultures. It causes iron or zinc deficiency and can cause an obstruction in your colon. It is particularly serious for a pregnant woman or children as it can cause mental problems and developmental delays. It can cause autism. Unfortunately it is most common in children.