Unknown to you, you begin to grow an udder on your belly. At first it seems like your just getting a potbelly, but soon 4 cow teats emerge. Then the udder begins to sag downward and then it begins to grow bigger as it fills up with milk, and soon it surpasses the size of a normal udder but still continues to get bigger. As it continues to get bigger the area of your skin that connects to the udder begins to move further up your body.
An hour later you are still suckling that woman's tit. But if you had even notice, you would have seen that you are now just a human head connected to a one ton cow udder.