There was a long list of negatives that affected the life of Native Americans as a result of the emigration of people from the East to the Western Territories.  One was the change in migration patterns and the resulting scarcity of their primary food, the Buffalo.  Native Americans were intelligent people who may  have been ignorant of the thinking of these European-American white people, but they were not stupid.  It did not take them long to determine that all of the constant hunting and interruptions in migration patterns and breeding of the great herds was driving their food away from their commissary.  Hungry, the leader of these warriors makes the sign of "eat," asking for food.   The emigrant signs "encampment."  I really don't know how this barter turned out. 

Hunger and self-protection are both strong motivators.