When Jacob was younger, he said "uh-huh" in response to every question we asked him. Now he is in his "no" phase. When someone does something inappropriate, Jacob will wave his finger at that person and say "no, no, no, no, no." Erin taught him to say "no, ma'am," which has become his favorite response to Dolly after she steals food out of his hand.
Sometimes he says no because what we're offering him actually is not what he wants. Most times, though, he says "no" because it's new and fun.
Here is an actual conversation I had with Jacob following a short run:
Jacob, do you want to play outside?
Do you want to play inside?
Do you want to play in between?
Where do you want to play?