When my mother was growing up in Smithfield, TX (near Keller), she lived on an active dairy farm. Her parents and herself raised and milked over one hundred cattle for a living. To do this, they lined the cows up in rows just within the barn, for their high-protein feed that helped the milk production. Then they would, of course, milk the cows.
From the feed area of the barn, one could look out across a grazing pasture, and literally see for miles. This was a Texas prairie, and nothing but grass was there. So one day the cows were all lined up and feeding, when suddenly, all their heads in unison, looked out toward the pasture. Then all the cows proceeded to follow something across the pasture with their eyes, and then calmly returned to their food. Remember, the pasture was flat, and everything that came across it would be clearly visible to the family tending the cows. Yet they saw nothing. So what did the cows watch?