Corn smut is properly known as Ustilago maydis, which infects the developing kernels of corn and transforms them into gigantic gray-black blobs, which look something like a brain made out of mushrooms. In Latin America the resulting blobs are known as huitlacoche, and are used as a filling. Corn tumors may not sound very delicious, but a lot of people swear by them!
Well it turns out that the joke's on us, because huitlacoche is incredibly nutritious! And, if prepared properly (and from a fresh source, not canned) many people swear it's delicious as well.