Buffalo were fast, strong, and often unpredictable, but Indians understood bison behavior and used that knowledge effectively. They knew that manipulating herds was easier than controlling individual animals. In late autumn, when most hunts occurred, bison were usually dispersed in small groups of cows and calves. After much planning and ceremony, scouts gathered these small groups into a critical mass of 200 to 500 buffalo and positioned them within a few miles of the sinkhole. When they sensed a threat, bison naturally tended to seek the apparent safety of a large group, so scouts gently harassed the small groups into one large herd without causing them to scatter, turn on their antagonists, stampede prematurely, or leave the area. Tribes also used decoys, such as a man covered with a buffalo hide who positioned himself near the herd and pretended to be a calf in distress; dominant cows would investigate, other buffalo would follow, and the decoy would move closer to the trap as the buffalo followed.