The hard object is often the cage itself. Rodents have bulbous eyes. Bulbous eyes bulge out like domes from the sides of the rodent's heads. Their bulbous eyes let them see in front and behind themselves without moving their heads. This helps them look out for their many enemies.
Most rodents have large eyes, especially the ones who are more active at night.
The families of wild rodents living in North America include squirrels, chipmunks, rats, mice, beavers, lemmings, muskrats, voles, and porcupines. There are more rodents living in North America than any other kind of mammal. They range in size from mice weighing less than three grams to the beaver weighing 49.5 kg. Only the capybura of South America is a larger rodent than the beaver.