What is the center of gravity?

Bubba decided it was time to purchase a new saw to help clear his heavily timbered property. A salesman showed him the latest model chain saw and assured him that he could easily cut three or four cords of wood per day with it. But the first day, Bubba barely cut one cord of wood. The second morning he arose an hour earlier and managed to cut a little over one cord. The third day he got up even earlier but only managed to achieve a total of 1 ½ cords of wood.
Bubba returned the saw to the store the next day and explained the situation.
"Well", said the salesman, "let’s see what’s the matter." He then pulled the cable and the chain saw sprang into action.
Leaping back, Bubba shouted, "What the heck is that noise?"