Pesachim 31: Chametz, Chametz, Everywhere

The Gemara's extensive probing of any which place that chametz could be in play. Beginning with chametz being used as collateral in a loan. And ending (this daf) with chametz being buried under a landslide. How far we go to make sure we don't use chametz on Pesach! Also: Destroying chametz and nullifying the rest of it, in case there is any more. Plus: Who owns the collateral?! And what is the role of the creditor with regard to it, especially in the context of a chametz collateral?