Taste play

I was munching my organic green apple as I took a book to read for Noah, putting my munchie aside.

As usual, after our story time, I let Noah play and handle the book if it's not too huge and picked up my apple to resume munching.

I ate and gently knock the apple against his forehead, cheeks and nose, and noticed him opening his mouth as apple approaches. Sure enough, he gnawed onto the remains of my almost eaten apple and tasted the sour flesh *smuack smuack*. His first sensory taste contact with sour is now ticked off. What's next?