The mere touch of the hand wearing the magical ring was enough to invoke the spell and make the swapping trade.
"Neigh," cried out Becky, she suddenly found she was a horse, a mare, and feeling the equine pangs of being in estrus.
She panned her eyes around, as turned her head and neck to look along her flanks, seeing her horse tail swing as swish. The coarse feeling hairs of the tail gave a tickling to where as a mare and not being human, she displayed her femininity. She shivered her body from head to tail, and felt then her different body begin to betray her normal feminine manners.
Coughing, and shaking her head, Sally the roan mare found her mind inside the head and her inside the body of a human. It was so different being a human, the clothing so binding, annoying her, making a free mare feel claustrophobic! Sally tried to whinny but having crossed the mental transferring of Becky, they exchanged each their memories, as both knew then everything about the other as they remembered their own pasts.
"Ha, hey, yes thank you, this body, your form feels quite delicate when compared to mine as me when a mare. I shall learn to appreciate being you, as much I hope you too like being a horse in season. This ring did the trick and how as why you wanted to become a horse is beyond me, but I plan to keep your body, I think I could enjoy the leisure pleasures granted to humans!"
A moment later and in walked George inside the stables, he seeing his Becky he said to her, "Come now, the stable groomsman has two fine horses waiting for us to ride, come now, leave that rattle red nag to her soon breeding session!"