Will has started to string words together to form phrases and sentences. He'll repeat things he hears or try to come up with his own ideas. Some things make complete sense, like when he said "Daddy go bye-bye. Mama go bye-bye too." Most things are more gibberish, with a few intelligible words stuck in: "Aba beju sehis Mama's juice buboo."
My recent favorite, however, was when he declared out of the blue: "I see a purple cat." (Except that it came out like "Ah see pur-ple tat.") And then, "I see a white dog." I momentarily worried that Will was hallucinating from the back seat, until I remembered that these are two sentences from one of his favorite books, Brown Bear, Brown Bear, What Do You See?