This flock of Boids are a lot like people, after being active a while they get lazy and like to eat. The problem is, if they eat too much they won't be able to fly. When you see them fluttering on the ground a lot you can help keep them fit by moving the mouse over them rapidly to scare them a little. But be careful, if you scare them too much, they will fly off! And remember, don't shoot the boids!