Echo Location - On a camping trip, the kids discover that Ari is really good at playing Marco Polo. Even without saying "Marco," a blindfolded Ari can easily figure out where Olive and Elinor are. How does he do it? They get a clue when they learn about echoing voices from a cliff face and understand that bats make a special noise only a few animals can hear that helps them know what's around them. Ears to You - One day while playing at the lake, Elinor and her friends notice something very interesting -- they can't see ears on some animals. That's so interesting! How do they hear? This question sets the kids off to explore, and they soon learn how frogs, fish and moles hear. Even though it looks like those animals don't have any ears at all, the kids discover they do have ears, but that they're just hard to notice, because they are good for hearing underground or underwater. Just like there are lots of different kinds of animals, there are also lots of different kinds of ears!