In Spiky Echidna, a baby echidna gets a piece of wire caught in between his spines. It takes a friendly possum to pull it out for him. The short-beaked echidna is a mammal called a monotreme (meaning one hole -- it has one vent through which everything, including eggs and waste matter, passes). Its young hatches from a leathery-shelled egg then stays in the small, backward-facing pouch until its spines develop. If it is threatened, an echidna will roll up into a spiky ball on hard ground or dig quickly into soft ground.