In the past, the Dayak were feared for their ancient tradition of headhunting practices (the ritual is also known as Ngayau by the Dayaks) . Among the Iban Dayaks, the origin of headhunting was believed to be meeting one of the mourning rules given by a spirit which is as follows:
The sacred jar is not to be opened except by a warrior who has managed to obtain a head, or by a man who can present a human head, which he obtained in a fight; or by a man who has returned from a sojourn in enemy country.[19]
Often, a war leader had at least three lieutenants (called manuk sabong) who in turn had some followers. The war (ngayau) rules among the Iban Dayaks are listed below:
If a warleader leads a party on an expedition, he must not allow his warriors to fight a guiltless tribe that has no quarrel with them.
If the enemy surrenders, he may not take their lives, lest his army be unsuccessful in future warfare and risk fighting empty-handed war raids (balang kayau).
The first time that a warrior takes a head or captures a prisoner, he must present the head or captive to the warleader in acknowledgement of the latter's leadership.
If a warrior takes two heads or captives, or more, one of each must be given to the warleader; the remainder belongs to the killer or captor.
The warleader must be honest with his followers in order that in future wars he may not be defeated (alah bunoh).