A mole is a concentration of melanin pigments deposited in the inner layer of the skin (dermis). It may or may not be raised slightly above the skin surface. It is also called nevus. It is usually congenital, hence also known as birth mark.
At times hairs grow on them. They may appear suddenly or change their size and colour suddenly. These changes may be an indication of cancer.
Melanin pigments are found in all animals, particularly in mammals. Several physiological and congenital conditions may induce formation of melanin in animals. Hence moles are found in animals also but they cannot be seen distinctly on them due to the presence of hairs.