Why do we fondle the tail of the

 Nandeeswara statue in the Sivalayam ?

We see the Nandeeswara statue installed

 in front of the Lord Siva in the temple.

In the temple, in the innermost chamber

 (Garbha sthanam) where the main image

of the lord Siva is installed and outside of the

 Garbha sthanam the Nandeeswara’s idol is installed.

The Temple construction ( Alaya nirmanam)

and the installation of the Deities ( Devata vigraha pratishta)

in the temple is completly  done according to the Sastras.

 The process of that takes three to five days

by strictly performing the sacred Homas,

chanting the Hymns of the Vedas and other Mantras etc.,

 Once the Alayanirmanam and the Vigraha Pratishta

 are completed  as per the Sastras, next day onwards

 (afterwards) the daily pooja and dhoopa deepas and

chanting the Mantras must be performed without fail.

In the Sivalayam, the innermost chamber,

the lord Eswara’s Idol or image is installed and 

outside of Garbhalayam infront of the lord Siva’s 

idol or Siva linga  the Nandeeswara’s idol which is

also constructed with the precious stone and isntalled there.

Here the Nandeeswara is not the Bull .

It is not belonging to that species.

The Nandi is the most obedient and

made respectful offering of his egoism to the lord 

 and also the great devotee of Him.

The Nandeeswara always stands before

 the entrance of the Mount Kailasa

of the place where the Lord Eswara dwells.

If we fondle the tail of the callte like cow, buffalow,

the bull, by nature they feel very happy

and offering their submission to us.

In  the Siva Temple, when we visit there,

all we compulsorily do the fondle

(treat with fondness) the Nandeeswara.

Then the Nandi feels so happy and do the Nivedana 

(appeal to the higher authority of) to  the lord Siva

 that  we, the devotees  have visited there to obtain

the darshan of the God and make us to have the darshan.

The   Bull (Ox) is the representation

 for the Dharma and so by doing the fondle

 ( treating with fondness) of the Nandi is the symbol

 for that we are instigating the Dharma and

 also shows  that we  follow the Dharma.