...his name! This is big news for me. You say "Jack" and he totally looks for you and wants to know what you're saying to him.
And he knows "reload" (meaning, give back the spoon so I can put more food on it), and that when I am singing Baby Beluga he will get a kiss on the nose after the part about the "little white whale on the go," which he is pretty sure is him. :)
Jack is all about sharing his knowledge and talents, too. Today we were visiting Caiden, and Jack gave him a bit of help from one cousin to another. He reached out, grabbed Caiden's head, and helped him to do his first tummy-to-back roll. Caiden was very surprised, but then he did it on his own a couple minutes later, so Jack's assistance was apparently very helpful and instructive. :)