Pancake Snakes

Describe a weird animal in your world. Why do people consider it "weird"?

Pancake snakes, or "pannies" are the sort of odd creature which makes one wonder how they survive and propagate. They have no fangs or poison. Their bodies are not built to constrict prey, and since slithering itself is difficult for them anyone who just saw one as they walked along would wonder how they weren't all scooped up by predators ages ago.
An adult pancake snake is about two feet long, with the middle of it's body flattened and spread out into a fairly circular disc roughly a foot in diameter. Their bodies are a tawny brown, with small jet-black eyes which can, in a pinch, blend into patches of forest detritus. They flop along with the same motion a manta ray uses to swim most of the time, and are frequently spotted because of this overt locomotion. Nobody is sure exactly what they eat in the wild, as specimens in captivity have tried to swallow literally everything stationary in their tanks smaller than their mouths.
How does such a strange creature survive?
Well, in the first place there's precious little that would eat a panny. Though the meat is fairly nutritious it doesn't taste terribly nice, and there's a million little bones inside that flat, round body. There are a few bird species which have evolved to simply digest sufficiently small bones, and these are it's main predators. However, in order to escape when under attack pannies have a special method of locomotion. The creature arches its back, bites into it's tail, and rolls away.
Weird, right?