Wombat feces naturally have a cubic shape.
Why it is true
Wombats are the only known animals to produce cube shaped feces. This occurs due to variations in the elasticity of their intestinal walls, which prevents the feces from rolling and helps mark territory on inclined surfaces.
Source: National Geographic
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.