Human skuls taken by the Konyaks - Mon - Nagaland.
Reasons for head-hunting are mainly 3 according to the anthropologists.
1) Retaliation
When one of the family members or age-group fellow got disgraced, it is regarded as a fair motivation for the whole group members to go for hunt. For example, if a girl became pregnant after joining the bachelor party (all night gathering at the festival for single boys and girls looking for a partner) and name a boy as her baby's father, he cannot deny, or he will become a target of head-hunt by girl's tribe and family. The only other options; either admit "yes it is me" or give her enough presents for compensation.

2) Dedication for God
Same reason as another Myanmar head-hunting tribe Wa has. Naga used to hung heads, arms and legs as a token of gift to the God and wish for therich harvest. In the book "RACES OF BURMA" originally written in 1933 and re-printed in 1997, following stories are shown;
Naga people spread the blood of hunted men around the rice field. Young child was preferred and bought for such sacrifice. Mr. Grant Brown also described in his book "BURMA RESERCH SOCIETY'S JOURNAL" June, 1911 issue that arms and legs were cut apart in the most horrifying way because they believed longer and deeper the pain and horror was, greater the God' return would be.

Naga people live in the between Hukawang valley and Assam, India had a custom of sacrificing boy or girl slaves for the better autumn harvest.

Victims were kidnapped from the foot of the mountain and killed in variety of ways, some by a spear or cut by the neck. Victims were usually given some medicine. Separated parts of bodies were shown to the public in the village. There is no evidence of man-eating habit.

3) Personal Glory
If successfully hunt a head of rival village warrior, he would be regarded as a real macho.

But sometimes head-hunting occurred for very unreasonable purpose. 50 years ago, in the village of Layshi, people were fighting against the Indian border village 10km far. One day at lunch time, Naga village chief in Layshi were not feeling good and ate only little. One of his warriors asked what was wrong. Chief said "I feel bad because you my warriors haven't succeeded to hunt our enemy's heads". So the warrior rushed to the border village and hunted 4 heads, regardless whether female or children and served them at dinner, which pleased the chief very much that he ate a lot this time.