First, Sally and Jason found their tailbones stretching out, with grey fur sprouting from their bases. They soon grew out into two long, ropey tails of similar length, with hairs at the end.
"Wow Sally, you've got a tail!", said Jason, trying to take his own attention away from his daughter's lewdness. But that only earned him a guilty sight of Sally's young buttocks. Sally was blushing too as she saw her father's butt, now with a furry long tail wavering over it.
As they marveled at their new parts, their feet came next. Their toes came together, with toenails fusing into one large, solid lump the color of charcoal, while their knees suddenly (and painlessly) snapped the other way, becoming more digitigrade like the hind legs of horses.
"We're...horses?" Sally questioned, as she looked down at her changing self. She and her dad were standing up on their new hooved feet. More grey fur sprouted on their thighs, as their butt cheeks swelled to larger size, and in between those cheeks, their anuses puffed up into beastly, fleshy black donuts. That made both father and daughter go even more red.
"Actually, I think we're going to be donkeys!", Jason remarked. "Look, our ears!" Sure enough, they both found their ears getting more pointed, before shifting to the tops of their heads, and stretching longer and longer, with grey fur on their backsides. Sally laughed. "We're donkeys!"
The ears finished changing. It seemed like things have stopped for now. Sally and Jason looked at the wall-sized mirror of their room, and saw they were donkey-people, with a donkey lower body and ears. However, they still looked quite human, with their torsos and arms mostly empty of fur. Their genitals also remained human-like.
But that was about to change.