Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com. E.N. Rittmeyer et al. (2012) - The Conversation What is the smallest animal ever? – Peter, age 9, Brookline, Massachusetts The biggest animal in the world is easy to see, if you know where to look. Living in every ocean except the Arctic, the blue whale is the largest animal on Earth — weighing as much as 200 tons with a heartbeat that can be heard up to two miles away. But the smallest animal in the world? Even if you knew where to look, could you see it? To track down the tiniest creature, scientists had to first decide what they were looking for and then, where they might find it. The first question – “What is an animal?” – is something that scientists have debated for centuries. I am an exotic animal veterinarian especially fascinated by these types of questions. What is an animal? In the language of science, an animal is an o...