Nobody messes with a hippo. Hippopotamus amphibius, the heavyweight champion of the Saint Louis Zoo's River's Edge habitat, weigh between 3,000 and 8,000 pounds, and they're always hungry. One of the most aggressive creatures in the Sub-Saharan or anywhere else, hippos can outrun the bejeezus out of the average human (up to an impressive 30 miles per hour), despite the fact that they're, you know, on the zaftig side. And while it's disquieting to imagine being sat (or chewed) upon by a hippo, there's something utterly calming about the ease with which the massive mammal makes its way through the water. It's big. It's beautiful. It's...graceful. Still, we wouldn't want it to sit on us.