As far as animals go, mammals are pretty much straightforward creatures. Their most defining characteristics include having hair, being warm-blooded and giving birth to their young ones alive, for the most part. But this group of animals which we humans happen to also be a part of has its fair share of oddities. Per appearance, some mammals just don't conform to the general rule and come out looking stranger than fiction. The armadillo is one such Mammal.

Armadillos are rather strange animals that inhabit various countries in the South American continent. They range from tiny species like the pink fairy armadillo to ones that grow to enormous proportions like the giant armadillo. Pictures below:
The name "Armadillo" is Spanish for "little armoured ones" and it isn't a name they bear for nothing. These animals exhibit a feature most commonly associated with reptiles and moluscs like turtles and snails. This feature in question is the presence of a protective shell.
Known as the only mammals to possess this trait, armadillo shells are composed of bony plates called osteoderms which are covered by scales composed of keratin, which is the material that makes up fingernails. Additionally, parts of the shell are divided by bands connected by flexible skin which allows the animal fold itself if need be. In most species, the shell covers the entire back and extends past their fore and hind legs, leaving the hairy underparts exposed and unprotected.
As seen in the images above, armadillos can curl themselves into balls when threatened, thanks to the aforementioned bands in their shells. They turk their legs into the shell while their armoured head and tail seamlessly meet side by side to form a sphere. Just how durable is this shell? Durable enough to occasionally Deflect bullets. Some people who have attempted to shoot at these creatures have learnt the hard way just how impressive they can be.
There is a rule in handling a gun that goes "Never shoot at a flat, hard surface", and this rule extends to the tough shell of the armadillo. One such case of bullet deflection, as reported by The Independent, is that of a man in Texas, USA who found an armadillo, regarded as a pest, in his garden and attempted to shoot it. He fired three shots and at least one of them ricocheted off the shell and hit him in the jaw. The man had to be rushed to a hospital and have his jaw wired shut as a result. The armadillo he shot was never found.
Another case given by the same newspaper source is that of a man who also fired a shot at an armadillo found on his property. But the bullet got deflected, hit the fence and went through the back of his 74-year-old mother-in-law's chair and struck her. Luckily, she was not seriously injured.
However, it should be noted that, despite the tendency to deflect bullets, armadillo shells are NOT bulletproof. This was clarified by National Geographic who debunked the claim of these animals being resistant to bullets. They hold that armadillos can, in fact, be vulnerable to attack. Deflection of a bullet is possible but it depends on many factors like the angle at which the shot was fired and the hardness of the surface, of which the armadillo shell is a sure fit.
But why risk shooting at this animal and injuring yourself and others in the process? There's more than one way to kill an armadillo, after all.