I think it started with the Nose Game (where you poke someone in the nose and it goes "Meep!" or "Boop!"). Daddy introduced Elijah to the Nose Game sometime before Christmas. Elijah took to it like a duck to water. It soon became his communication of choice. The Nose Game is played only with people that Elijah likes - no strangers. It can have as varied meanings as "I forgive you", "I feel better now", "Wake up, sleepies!" and "Thank goodness you're home!"
Then it moved on to the belly. We'd tickle Elijah's belly during nappy changes and say "Belly, belly, belly". Soon he started trying to tickle his own belly.
Then suddenly, we realised he also knew where his head and eyes were. He would point to them when the words were mentioned in a sentence. He would also point them out if we asked him where they were.
So we thought we'd ask Elijah where some of his other body parts were. He knew toes as well!
In the past week, Elijah's understanding of anatomy has grown to include the identification of hands, knees, shoulders (though he usually points out our shoulders instead of his own), ears and mouth, all pretty much without any effort on our part.
So we now know all the body parts required to sing Heads, Shoulders, Knees and Toes, including the facial features section, with the actions. That's going to be fun!