"If we must, we must," Kat said to Dan, as Dan stood there shaking his head and replied, "No way, not me, never, you will have to work out your sexual frustrations with someone else!"
"OK Mister Obstinate, then with my wand I shall change you to feeling for me a dire need to be pleasing." Kat said, as Dan seeing the wand pointed at him, he was about to call for their mother, when.... FLASH!
"Its not permanent bother dear, but it seems to cross fit the way we need to survive. Now you are mine and I shall use you to thrill me. Say what, did I hear you ask what just happened? I made of you as a living dildo, my brother being a jackass, is for me a donkey cock size dildo to pleasure me.... Oh, oh what is this, what is happening to me, I, my vagina is on fire...!
Oh, oh what is it my sense of lust is going wild, I know I need you inside of me, you a donkey cock sized dildo, but my body, ah..., yes you do quell the urges, ah Hee-haw, what?" Kat said, as her last lusty thought pulled out of her mouth a braying Hee-haw.
Wild invigorating moments together and the spell swirled to engulf both Dan and Kat as the dildo grew and matured to become a brown furry donkey Jack-stud, and Kat grew to become for her stud as a jennet donkey in the throws of estrus. hey in her bedroom stood jackass shoved tight up inside his sister donkey, they rutting together more than just once, but remained as beasts for the whole day, the night, and into the next day before returning to being people at high noon.
"Kat," their mother yelled from downstairs in the kitchen, "You made your bedroom as quite the mess, now clean it up!
Dan, you go and shower, likely you stink like a Jack donkey from having bred your sister some dozen times!"