I think that's a key trade-off in duck typing and reopening classes and objects. You get immense power to do "cool", powerful, and useful things like that, but at the cost of debug-ability.

It's been a while since I really used Ruby in anger but to discover where these things came from you need to just look up the documentation of your dependencies and their dependencies, and see where something got added to. For me most of it came from ActiveSupport, and I ended up using that library by itself in other projects than just Rails.