It is said that man and mithun were brothers. However, mithun was the lazy one and slept all day long while man toiled in the fields. All attempts to make the mithun work failed.
"You have to work, brother," man told the mithun.
"I don't feel like working. Let me take rest," the mithun said.
"If you don't work," man said, "will you eat grass?"
"I would eat grass rather than work," the lazy mithun retorted.
"In that case," man yelled at the mithun, exasperated, "We cannot live together. Go your own way."
The mithun realised the gravity of the situation, but still did not offer to work. He requested the man to let him live in the village, but man was adamant. "No way. You have to go away," he said.
"Where will I go, my brother?"
"You can go to the jungle as you wanted to eat grass!"
"I love you," the mithun said with tears in his eyes. "I cannot live without seeing you."
Man was touched, but was not ready to live with the mithun unless it worked. Seeing the man unmoved, mithun begged, "I will go to the forest, live there and eat grass. Can you please come to my place sometime to see me?"
"If I do that," the man said, "What will you do for me?"
"I will go to the places you cannot and even die for your cause."
Man agreed to this condition. Till today, he owns the mithun and goes to the jungle with salt to feed his estranged brother. In return, the mithun is sacrificed during festivals like Murung and Subu. They are sacrificed during other rituals as well.
On the occasion of Murung or Subu, the priest chants all day long telling the mithun, "We are sending you as a messenger to the other world where man cannot go. Don't hold me guilty since it was your own words. I am simply fulfilling the wishes you made in the days gone by."
No wonder the Apatanis consider the mithuns sacred and they are sacrificed only during very special occasions.