All three types of cassowary have a horn-like helmet called a "casque" on the top of their head. The casque is a keratinous skin (like a finger nail) over an inside made of firm, but foam like material. This material can be bent and squeezed but it goes back to its proper shape. The name "cassowary" comes from two Papuan words meaning "horned head". The reason for the casque is unknown. There are a number of different ideas, such as: