Nandi Bull (Vahana of Lord Shiva) in seated posture statue made in Parad (mercury) to place near Shivaling, or to take home tample.
During the churning of the ocean when poison (halahala) came out everybody ran away except Lord Siva, followed by Nandi, came forward to help as He was the only one who could counteract this deadly poison. Shiva took the poison into his hand and drank it, the descent of the poison was in turn stopped at His throat, by His divine consort. Shiva is therefore also known as Nilakantha (the blue-throated one). Nandi saw some of the poison spill out of Siva's mouth and immediately drank it off the ground. The devas and asuras watching were shocked and wondered aloud what would happen to Nandi. Lord Siva calmed their fears saying, "Nandi has surrendered into me so completely that he has all my powers and my protection".
Nandi represents strength, faith, and constancy in belief. Images of Nandi often sit directly outside a shrine to Shiva, facing the deity. Often an image of Nandi, the sacred bull on which Shiva rides, faces the linga. Nandi signifies single-minded devotion and the peaceful strength of faith. Nandi is the protector and guard of all Shiva Temples. Nandhi Devar share several characteristics like Lord Shiva, hence the title of Eashwarar has been bestowed on him. Dharma or Righteousness is personified as cow and with maleness added, Nandhi is the official guard of Lord Shiva.
As per the Brahma Purana, any person, male or female and belonging to any "Varna"- Brahmin, Kshatriya, Vaishya or Shudra, who worships Parad idols daily is blessed with worldly pleasures and lastly achieve supreme salvation (Moksha). The Parad Idol gives to worshiper a life full of beauty, honor, fame, happiness, knowledge, and wisdom.
As per the Vedas, there is nothing more pure, pious and auspicious in Kaliyug than Parad. Parad is also found effective in controlling various diseases like High Blood Pressure, Asthma. Parad has special significance in Ayurveda too. Many ayurvedic medicine use parad as the chief ingredient for giving energy.