Preston found perhaps one of the most arresting scientific papers published this year, a report on 10 hippo-neutering procedures European and Middle Eastern veterinarians performed. She describes the challenges of hippo castration, none of which I would have guessed. For example, did you know that hippos' testes are located inside their bodies, unlike, say, the testes of humans and most other mammals? The paper Preston reports on, published in the journal Theriogenology in October, calls hippo testes "spatially dynamic." That means they actually move around within the hippo body, sometimes after veterinarians have located them with ultrasound and gone in after them, surgically.