September 27, 2006—That barking dog next door might sound loud to you in the middle of the night, but you haven't heard what a ruckus animals can really make until you've heard howler monkeys do their thing.

Journey to the jungles of South America, and hear what scientists say is one of the loudest animals on Earth. Then stick around to learn just how and why howler monkeys manage to make such a commotion.