when a large group of natives capture you, tie you up, and begin so slather mud/poop on your body,(commonly the penial area). after the mud/poop is slathered they bring in the tribe cheif who gives the victim a vigirous Hand Job.
Guy: hey man how was your trip to the Amazon?
Friend: it was great, i met some natives, they gave me a souvenier.
Guy: what was it?
Friend: an Amazonian MudBall!