Frogs

I'm having a problem that I have had before. Frogs. Not that I have anything against frogs. In fact, I rather like them. But the problem is, how do they get into my back yard? The yard is surrounded on all sides by walls that are at least ten feet high. That would seem to rule out the possibility that they come from any adjacent property. So, how, then? Do they fall from the sky, snatched off their feet from elsewhere and randomly deposited at the whim of the wind? I think not, because 1) What are the odds that so many would randomly choose my yard to fall in, and 2) What are the odds that they would survive their landing? Perhaps they arise from a sort of primordial soup that brews in the yard during rainy season. But in this case, wouldn't they need a few million more years to actually emerge as frogs? Do they tunnel up from the center of the earth? I would say not. These are clearly not the tunneling sorts of frogs, if such a thing even exists. They're not even very good at hopping compared to the common American frog. Yet they do hop, as well as they can hop, and happily so, whilst I lay awake last night considering them. Oh well, I had nothing better to do -- other than sleep, I mean.