My first thank you

The other morning, Luke sat in his high chair waiting for breakfast.  As usual, I began by filling his cup with water.  When I gave it to him, he said, "thank you!" It was the first time he said it without prompting or simply repeating it.  I was so excited to hear my little guy using manners already!  So now we are working on please, both the word and the sign.  I didn't feel like I taught him to say thank you, but I guess it all goes in.  It's probably just repetition and imitation, and now I am so glad I use manners myself!