She thought it would be fun to do some "pet" play. Cats were her thing. She envisioned herself rubbing herself on her naked boyfriend as foreplay until he could stand it no longer. What she didn't imagine is that the collar, from that quaint little shop, was magic and had a solid long-lasting curse on it. After putting it on, she felt a strange tingle around her neck. This spread throughout her body. When it became intense enough, she was no longer able to stand. On all fours, she discovered a slow conversion of her legs and hips into that of a cat! Her teeth and tongue were also changing.
When her boyfriend showed up three hours later, she was a sphinx - a large cat with several pairs of human breasts of decreasing size. Even her face had light fur and, when he entered her apartment, she pounced on him even before he had a chance to take his coat off.