While mummies are normally thought of as humans, it was also common for Egyptians to mummify animals. This was for a variety of reasons. Sometimes, animals were brought in the home to live as pets, and they were mummified when they died and were buried. Other times, animals were mummified to be sacrificed or offered to humans for the afterlife. When animals were mummified in ancient Egypt as a sacrifice, they were able to be bartered or purchased. It is believed, after studying mummified animals, that partial remains like feathers from birds were sold instead of full animals. Over thirty catacombs have been found filled with mummies, all dedicated to one particular animal. All types of animals, ranging from crocodiles to cats, have been found in mummified form.