By not giving them any rights even though complex expression through language implies a high level of intelligence and sapience. The dog and cat that you can still talk to are still considered your property that you can just take to the vet and put down. Animal shelters can now just tell the animals their kill dates so they don’t get too hopeful. Slaughterhouses will be filled with screams you understand instead of just screams. Cosmetic companies and labs can now ask their test subjects for the level of pain while smearing makeup in their eyes. Sea World, zoos, circuses, etc would make peak profits now that they can address their slaves as if they were human slaves.

I mean, all humans can communicate with each other and we still don’t give rights to some of them. Anyone who thinks we’ll be nice to animals just because they can talk is either a child or otherwise doesn’t know how humans operate.

By telling them lies just to complete some experiments

use them as insults.
“wow you eat like a pig”
🐷??? “and thats a problem why?”

also tell them how we treat them and see them as lesser beings compared to us.

Ask for consent.

We would make it too complicated. Almost all animals are in survival mode. Some that have free time could understand limited concepts. It would be easier to setup commerce with some corvids for example but not to keep them out of the corn fields. Dogs would have a lot more anxiety and cats wouldn’t change much.

Considering that negotiating with livestock would be a hassle, probably just pretend we can’t understand them

Telling them that man is the image of god and they are inferior beings created for man to subjugate.

Advertising specific to animals blasting all the time everywhere

Spend hours trying educated them democracy and war and watch them break into faction to murder each other