Cogito ergo sum. You only need one sample to prove existence of a thing. As for the rest, communication. I can share information with other people and debate

Cogito ergo sum. You only need one sample to prove existence of a thing. As for the rest, communication. I can share information with other people and debate this. That's not possible with a river. Animals are in between, they can clearly understand some things but not everything. Moreover we can point to an ability to process things that predicts this difference in our ability to communicate.