It is important to remember that the tortoise does not live inside a shell, it is a shell: tortoises walk like they do because the sockets of their hip and shoulder bones are inside their shells, right at the top. They move like we would if we were cars with arms and legs: slowly, and not like cars at all.
Their shells are part of them in another way, too: they have nerve endings, which is why tortoises enjoy being cleaned with toothbrushes or showers:
