CrowdScience listeners come in all shapes, sizes and ages. This episode is dedicated to our younger listeners who, as we’ve learned before, are experts at asking those superficially obvious questions that for parents, are anything but easy to answer. To start off with, Sylvia, asks why elephants are so big? As we hear from our expert – mammals were at one time, much larger – so perhaps the question should be, why aren’t they bigger? We investigate what drives body size in the animal kingdom. Presenter Marnie Chesterton, together with our ‘cub’ reporter Arlo, goes in search of the most brilliant scientific minds to respond to a slew of other queries. Shambhavi, from Singapore wonders why humans have five digits on each hand? And Benni from California asks why dogs don’t get sick when they drink from muddy puddles? Do dogs have some amazing ability to fight off viruses and bugs? Beyond the confines of our planet, we’ve also got a question from Olivia, from Sydney, Australia, who regularly contemplates the universe: what is the biggest object in it she wonders? Marnie and her experts do their best to solve these mysteries. Presented by Marnie Chesterton, produced by Dom Byrne for the BBC World Service. Image: Getty Images