When my youngest was in a walker - less than 6 months old - I answered the phone with the usual "Hello." greeting.
A second later I heard her say "hwo" - one syllable. I wondered if she was saying hello. The phone rang again a bit later, and the same thing happened. She was saying hello. I started listening and soon realized she also said 'behsu' (bless you) when someone sneezed. No doubt it was stimulus response, but it proved to me that our little ones start learning from our example at a very young age.
I'm sure my older two were similarly talented at that age, but I never noticed.