What if the sentient species on the planet was not man? What if something smaller had evolved to our position? By smaller, no smaller than ants, but no bigger than the average rodent (chipmunk, mouse, etc.). If this is scientificially reasonable (if not, I guess this would belong in the ASB forum)?
Main point of interest is infrastructure and technology. For example, at what point would they be able to build bridges?? Would they be able to build cars and rockets? What about ships? Even small waves would be able to take out rodent scale ships. And think of all the predators they have. They might purposefully drive some species to extinction when they get the chance, if only to save their own hides.