My mom has always believed that we shouldn't underestimate children. When I was a baby, she used to talk to me as though I was already grown and could tell based on my reactions that I understood what she was talking about.
Granted, weren't discussing nuclear physics or anything, but other adults seemed to wonder why she was bothering to talk to me about the average things going on in our lives.
And indeed, it seems that when we talk to babies, they listen because the full video shows what happens when one dad keeps his son engaged like that.