Caganers are small figurines traditionally placed in Catalan nativity dioramas. Here's an example of one: it's tucked into the background, in the bushes left of picture.
A caganer is a little man or woman, sometimes a famous personality such as Barack Obama, Angela Merkel or the current Pope. Often, it's a more traditional little man in peasant garb - brown trousers, shirt, red Phrygian cap.
But all caganers do two things; squat with backsides bared, and defecate.
"Caganer" is Catalan for "shitter," and it is a Christmas tradition to insert one caganer in every nativity play.