Weaver bird uses its beak to weave the other fibers together. During the weaving process, it calculates the required tension as the nest will collapse if it's too weak. The bird also needs to be able to visualize the finished structure, since while building the walls, it must determine where the structure needs to be widened.
After finishing the weaving of entrance, it proceeds to weave the walls by hanging upside down and keeps on working from the inside of the structure. It will push one fiber under another and pull it along with its beak, until it accomplishes a stunning weaving project. Nest is done finally. It hangs from a tiny, swinging but strong twig, with an opening from the bottom part, which brings extra protection to the nest.
The weaver bird won't just begin building its nest. It proceeds by calculating in advance what it needs to do next – first, collecting the most suitable building materials, then forming the entrance before going on to build the walls. It knows perfectly well where to thin or thicken the structure, and where to form a curve. Its behavior displays intelligence and skill, with no trace of inexperience.
With no training, it can do two things at once – holding down one end of the fiber with its feet, while guiding the other end with its beak. None of its movements is coincidental; its every action is conscious and purposeful.