Rob was now sucking greedily from Mary's udder, oblivious to the fact that his body was filled with milk up to his neck. The weight of the milk was more easily pushing Rob's rubber body outward.
Rob's stomach ballooned outward in a mad attempt to hold in the incoming milk. The weight made it sag. Unable to keep standing, Rob fell with a slosh. He didn't have far to fall, his stomach had swelled out far enough already that he'd become nearly round.
Mary's udder was shrinking, all the milk going into Rob. A moo came from Mary as she felt the pressure lessen. Rob continued to suckle, his belly had ballooned outward and was now overtaking his arms and legs. They fattened up and were slowly merging into the ball of his body.
A good thirty minutes passed with Rob sucking Mary's udder dry. Mary pulled herself out of Rob with a wet pop. Most of her milk was gone and she could move again. Rob, still in the ecstasy of the milk kept sucking.
Mary fondled Rob's rubber cat ball body. "Thank you Rob, that was...wonderful."
Rob's dazed eyes grew focused again and he realized what had happened. He couldn't move, he was filled to brimming with milk and round as a balloon.
"Oh, my, what have I done?"