"...a what?"
"Of course, I forgot who I was talking to. It was a fad among magic users with human friends some years ago, but it had little commercial penetration, due to the fact that unlike most uses of human or demihuman souls, it requires a willing sacrifice. For the same reason, however, when they do reach the market, they command a high price."
"You're going to sacrifice me?"
"Of course not. I'm going to sell you. You're going to sacrifice yourself." Meredith took out a pound coin. "When you take this, you will fall limp, as you will whenever someone sells you forevermore. Given freely, however, by your lawful owner, you'll wake up, and from then on take on any inanimate your new owner suggests, provided it's human or smaller size and not too complex - no buildings or computers. When animate, you won't be under any compulsion, except that it will never occur to you to escape, and of course, you can be inanimated if you get too unruly."
"Lawful..." said Nicola, "how is any of this lawful?"
Meredith laughed. "Child, you will find that I - and now you - are subject to a law far older than any ephemeral human king or moot."
"And if I'm stolen and never found?"
"If your lawful owner dies intestate, you'll devolve onto yourself, going dormant if animate. You'll then be able to give or withhold your blessing to any transaction your possessor makes, selling you or giving you - until you do give one your blessing, of course, since then you'll be owned again."
"Forevermore, you said - so I'll be immortal?"
At that Meredith paused. "You know, I'm genuinely not sure. Animate, you can be killed, but you won't age, and damage to your inanimate or dormant forms won't do permanent harm, nor will damage to your animate form that doesn't kill you. If you were human, without a buff, you would fall dead or forever inert on your hundred and twentieth birthday. In your current form, I don't know. It's good you mentioned it, because I'd almost turned you back, but now I think I could get a few hundred quid more for the novelty."
Her big mouth. Well, there were certainly worse fates that could befall her if she kept playing the witch's potion game. "All right," she said, "on the condition you let James go."
Meredith took some steps forward. "My dear girl, you are in no position..." she put a foot down between Nicola's legs, so close to her sex that she flinched instinctively, "to make demands." Meredith smiled as Nicola stared at her foot. "But I'm in a generous mood," said the witch, producing a wand. Instantly, James collapsed to the floor, human. He stood up, eyes burning holes in Nicola's bare body.
"Out," said Meredith. "And don't come back."
"But Nicola..."
"Forget her. Her life going forward will be far more pleasant than yours will if I ever see you here again."
After a look at Meredith's stern face, and a long lingering look at his friend ('s breasts and vulva), James ran for the door, as quickly as he could with his muscles still asleep. It dawned on Nicola that she'd never see him again, at which time she was hit by the sobering realization that the same was true of everyone she'd ever known.
Meredith smiled and extended a hand. "All right." Nicola looked to see she hadn't palmed the coin, but she held it up in her other hand with a laugh. "Willing sacrifice, remember? I can't trick you. What would it matter at this point if I did, anyway?"
Nicola used Meredith to steady herself on her new hooves. She realized then that her tail could help her balance without her even being conscious of it - that would be handy, if whoever got her let her walk around for any length of time. Meredith held out the coin. "So before we get on with it, what should I call you?" she asked.
"Nicola." With that, Nicola took the coin in her hand, and it disintegrated as she fell in a heap. Meredith wrapped her in a broad red ribbon - it would rot when she woke up, of course - with a label reading "Nicola - £9,666."