There is no "ground" in the Smoke Ring; it is a world consisting entirely of sky. Thus, most animals can fly, even the fish. Furthermore, since the Smoke Ring is in orbit, it is in free fall. There is no "up" or "down", only "in" or "out" from Voy. Humans moving in the Smoke Ring use a poetic adage to aid their understanding of orbital mechanics - "East takes you Out, Out takes you West, West takes you In, In takes you East. Port and Starboard bring you back". (In the novel, the characters also say: "North and South bring you back").