If one harms another person's nahual, one may harm the person who belongs to that nahual. During sleep, the nahual can go wondering, something that can be seen in the dream. Nahuals can also be sent out to perform tasks, use it as an adviser, or a person can change his shape to that of the nahual.
The origin of the nahuals lies far back in pre-Hispanic times. Many patron deities of towns have their own nahuals to help them guard their towns, just like their pre-Hispanic forebears. These nahuallies make nocturnal patrols, giving off evil airs to ward off rival nahuallies. In ancient times, each day sign of the divinatory calender had its own personal nahual or deity, which corresponds to the present-day beliefs that each sign of the zodiac has its own nahual. Among the Quiché Maya (K'iche') the day a child is born determines its nahual, but the child is only told when it has reached a responsible age so that they may not blame bad deeds on the nahual.