Now I'll try to bring more physics into the picture. According to physics, everything that happens is because of the interactions of elementary particles. The birds flying around are complicated assemblages of atoms which have a lot of rigidity and which move because of internal releases of energy, and the stiffness of the molecules and the flows of energy ultimately result from lots of electrons and quarks interacting in their specific ways... Maybe it would have been simpler to talk about planets orbiting each other. :-) ... But whether it's planets or birds, the holographic description has to extend right down to the atoms and the subatomic particles. Every particle must have its image on the boundary. And here's the really interesting thing: Just as we have the ordinary physics of electrons and quarks which determines how they interact inside the space, we can define a different "physics" which applies to the holographic images of the electrons and quarks moving around on the surface of the space, which also makes the larger images of atoms, birds, and planets move around appropriately (changing size, and passing through each other without interaction if they are at different sizes).
I will add a further detail, at the risk of confusing you with too much new information, just to emphasize the difference between the "physics on the boundary" and the "physics in the interior". In string theory, electrons and quarks are indeed little strings that vibrate and move around. Those strings will have their holographic images on the surface, as in the picture in Juan Maldacena's article. But in the surface physics - the separate set of rules which describes in a self-contained way how the surface objects move around - the strings are not fundamental, they are condensed out of fields that live on the surface.
So if we back away from all these details and review the big picture, what do we see? We have a world of objects moving around in space - atoms, birds, planets - according to a fundamental physics of electrons and quarks (that are actually superstrings). We also have the holographic projection of all those moving objects onto an imaginary surface enclosing that region of space; and we have a different physical theory, describing the interaction of fields confined to that surface, in which the fields condense into strings which form structures which behave exactly like the holographically projected images of the atoms, birds, and planets. In other words, we have two apparently equivalent descriptions of the same physical processes, built up from theories of fundamental physics which are distinct and yet completely equivalent; but in one theory, the sphere has an inside, while in the other theory, we only talk about images moving around on the surface, not inside it.