Serapoh was told by spirit/antu Apai Puntang Raga about the correct rule of mourning the dead:
6. The sacred mourning jar is not to be opened except by a warrior who has managed to obtain a head; or by any man who can present a human head which he obtained in a duel; or by a man who has returned from a sojourn in enemy country.
Serapoh killed a Kantu boy which he exchanged with a menaga jar to open the morning jar and to end the mourning period.
This killing started the headhunting war between the Iban and the Kantu tribe.