Rob, a ravenous pig eager to eat more than his fill, knelt in front of Mary's large and nearly popping udder. With his fat rear sticking up in the air, Rob gently engulfed Mary's teat in his snout, slowly but surely moving it down. He reached up with one half-hoof to squeeze the teat.
A huge gush of warm milk shot into Rob's mouth. He grunted noisily as he worked the teat, sending jets of milk into him. The warm milk tasted and felt wonderful. It was filling him up, but he didn't feel full yet. He kept on drinking the milk.
Rob was so focused on the milk that he didn't notice the slow changes to himself. Mary's milk was apparently very fattening as Rob soon started to gain pounds by the minute. His already tight clothing was soon strained even more. First his shirt ripped and fell to the floor. His pants gave a harder fight, but ended up torn just the same. Rob knelt there, his piggish body all soft curves of flesh and fat. His arms and legs shortened, becoming more pig than human. A curly tail bobbed up and down with Rob's milking thrusts.
Snorts and oinks accompanied Rob's drinking. He kept drinking and kept fattening out. Mary's udder started to shrink down to a more normal size.