First, a large part of Jeff's transformation was a mental transformation.
From the outside, the behavior of a puppygirl would look incredibly cute. Unlike a human girl, a puppygirl actually does have an inferior intellect, but in spite of this fact, they still have a basic capacity for simple speech. Even the dumbest puppygirl can learn Ogden's Basic English easily, but beyond this, too many big words would make it confused and distracted. Furthermore, puppygirls are absolutely submissive and worshipful toward humans: they are ever eager to show how obedient they are toward their masters, slavering like kobolds at the feet of a dragon, and it is both hilarious and heartwarming how hard they try to prove they are good little girls. What they lack in brains, they make up for in love.
From the inside, the Chronviac's changes to Jeff felt a little bit different than they might look from the outside, and it kept Jeff fully aware of these changes throughout the process.
As Jeff's mind gradually collapsed in on itself, the first thing he noticed was that there were too many words swirling in his mind, and all of a sudden, he realized this was very annoying. There were too many to keep track of, and he just wanted things to make simple, plain sense. He was becoming closed-minded to all of these big words. As his mind drifted away, he had a momentary realization of why closed-minded people tended be kind of dumb: they just wanted a smaller number of ideas to deal with. Perhaps this was what it meant to be dumb.
Becoming dumber didn't feel terrible, though. He wondered why he once thought it would. It's just easier. As confusing, complex thoughts gradually gave way to simpler ones, he admitted that he felt kind of helpless without his former big, powerful intellect, but on the other hand, it felt...more manageable, he guessed. Less confusing. Less frustrating. Less tangled. In a way, he kind of liked it. Compared with what he had been before, he felt humble and simple, even more honest. Like all simpletons, he was oddly proud of his newfound simplicity. Even though he felt a sense of loss as the Chronviac took away his intelligence, he felt grateful as it also made him more earthy and real.
Nevertheless, the knowledge of how helpless this made him left him feeling incredibly naked. If he were turning into a wild creature, he would have the instinct to hide from big, strong, smart humans. For a fleeting moment, the thought of a big human towering over him and feeling so smug and superior really made him feel angry. The nerve of those creatures! Strutting about with such big brains and stomping on everything in their paths! This passed, for it is only the stubborn and truly contemptible fool that resents the wise.
The transformation from an independent creature to a submissive one felt just as unexpectedly comfortable as becoming dumber. No, that was not right: it was just as uncomfortable, but instead of the clawing rage of not being as good as a human, he felt an equally clawing desperation to be accepted by one. He wanted to be good. His mind was becoming utterly obsessed with being good. Being seen as good and being good suddenly meant so much. He wanted to be a good puppy. He wanted acceptance. He wanted love. As his mind became more submissive, he realized that he no longer resented those that were better than himself. Instead, they made him feel safe. With this change, the Chronviac made him into that heartwarming sort of fool that realizes that wiser people are there to protect and guide simpler people. Even as his mind shrank, his heart grew. In short, Jeff gained that quality which distinguishes an annoying moron from a lovable moron: humility.
(Pardon the digression, but one of the greatest curiosities of human nature is how the trait of humility interacts with the trait of intelligence. If one is intelligent, it is perfectly alright to be arrogant, and in some cases, it is even quite necessary. After all, could Frank Lloyd Wright have tranformed American architecture if he had been humble and apologetic? He was quite pompous and abrasive, but he could pull it off because he was also an authentic genius. Likewise, the opposite combination has a uniquely endearing quality, and such personalities can even be therapeutic to know. Pardon us, but there is something we slide-rule-packing, social-skill-lacking, pedantic nerds just plain like about dogs and dumb blonds. They agree that those that lack intelligence should consider listening to those that do, and it could not possibly hurt the human race to populate the world with individuals that harbor this belief. Such interbreeding between the IQs could only be eugenic.)
Finally, his mind became increasingly female. He was not sure how to describe it, though. Perhaps it would be easier to describe it in the sense of comparison: the male brain tends to feel a craving to take up space and to spread out one's presence and leave something permanent and unchangeable, but the female brain tends to want to move out of the way, weaving around things, wrapping itself, accommodating, and moving with a sense of flow. A female brain prefers to be more mysterious and magical. In a way, a female brain has a spiritual similarity to a stage magician and aspires to create illusions, which might explain the make-up. However one describes the sensation, Jeff was becoming less of a "he" and more of a "she." As with the other changes, it was distressing on one hand but pleasant on the other, being an alteration of trade-offs more than any real loss. He...she...was a beautiful, shining thread, waiting to be woven.
Jeff was still an embryo, though. He...she...was a magically a conscious fetus, but...she...was still a fetus. Being inside a womb and bathed in amniotic fluid felt good against her bald, naked body. It was like being in a hot-tub, combined with the feeling of an endless orgasm that never EVER seem to end.
Eventually, though, it would as all pregnancies must.
As Bella lay panting on a pile of blankets within her owner's house, her owner was greeted with an amazing sight, which he would have to keep a carefully guarded secret for his entire life. Bella was giving birth to something truly unusual. She was giving birth to an entirely new sort of creature. It was neither human nor animal, but it was alive and beautiful and screaming the tiny, haunting cries of the newly born as its naked body lay helpless on the blankets.
She was adorable. She was...a baby puppygirl. She might need a new name, though.