Nandi bull is the Vahana or the living transport of Lord Shiva. As a matter of submission and humility, the tail is tucked in, and the feet and face are in repose. It is a charging bull made tame by Lord Shiva. Nandi represents a devotee (of Shiva) whose passions are under control and whose devotion to Shiva is perfect.A statue of Nandi can often be seen watching over an alter to Shiva or at the entrance of a Saivite shrine. So most devotees pray first to her first born Vinayaga, that there should not be any obstacles while praying to Lord Shiva in his Koil (abode). In Sanskrit, the common bull is "vrisha", meaning : righteousness or Dharma. So it is important to seek the blessings of Nandi also before one proceeds to worship Lord Shiva.