They roll into a defensive ball when they feel threatened
The echidna is a monotreme, a mammal that lays eggs as opposed to giving birth to live young. Among living mammals only the platypus and the echidna are monotremes and both are indigenous to Australia and New Guinea.
You can see the face in this photo
Did you know that male echidnas have a four-headed penis? During mating, the heads on one side "shut down" and do not grow in size; the other two are used to release semen into the female's two-branched reproductive tract. The heads used are swapped each time the mammal copulates. Fascinating.
It's not often one gets the chance to get this close to an echidna in the wild so I felt quite privileged.
Oh, and before you ask, I didn't roll him over to check out his four-headed penis.