Would it not be fun to have talking, actually thinking animals around? There is some really weird logic saying that it can be done, for some really unexpected reasons! The reasons will at first seem totally unrelated to the conclusions, so please read first and think later.
Why it can be doneEdit
There is evidence that human children start exploring the world in a qualitatively different way from apes at the age of one and a half years (reference: Human Ape), which is the same age as they both start speaking and as their brains change into a distinctly human form (as opposed to the elongated form of ape brains). The assumption that it should be the distinctly human brain form in itself causing the effect is, however, refuted both by the fact that the breakthrough in innovation came only 50 thousand years ago while the distinctly human brain form formed 200 thousand years ago, and by the fact that some severely brain damaged patients are symptom-free and behave in the human way. The breakthrough 50 thousand years ago also happened to all Homo sapiens at the time no matter if they lived in Africa, South Asia, the Middle East, South-East Asia or Australia, making both genetic mutation and independent cultural innovation from the same much older capacity extremely unlikely. Rather, some completely unknown quality just happened to invade a Homo sapiens brain, and then started recognizing all Homo sapiens brains as livable redepositories. If the same quality can be made to invade the brain of another species, it will also invade all brains of the same structure as that species have.
How to do itEdit
Doing it by inserting human cells into animal embryos would not be enough. If too few cells were inserted and the brain structure did not become human (i.e. the brain structure human children get at age 1,5 year), the brain would not become a redepository (which is also confirmed by the non-sentience of animals with partly humanized brains already created in experiments), while massive numbers of cells inserted (giving the brain a human form) would only make that particular brain a redepository and not cause a recognition of ordinary animal brains as redepositories. Instead, it would work to insert more and more animal cells into a human brain (starting at an age older than a year and a half, when quality X is already there), thus getting the quality used to an animal brain structure. For the structure to change properly, the insertion of animal cells would have to replace eliminated human cells. This could be done by simply swapping stem cells used for treating dementia in humans for animal stem cells when the doctor does not see it. Even we crazy people understand that it would cause an overpopulation and food disaster if all animals in the world became sentient, but some sentient animals would be fun. There is a risk that governments would try to wipe out the sentient animals, but that can be solved by directing the project at making cows sentient. Cows are considered holy in India, which is the second most populated country in the world (after China), with a growing economy, a space program and some nukes, so not even the United States would launch a cow extermination in India even if the cows became sentient.