There have been a lot of big changes in the last month, most notably WORDS. It took him a bit longer than his sister to start talking, but he's really making up for lost time. One word he still doesn't say is his sister's name (or any approximation of it). Instead, he uses this sign that he made up for her, I think because she kisses him so much on the cheeks.
On the bike ride to school, when she's not on the bike chattering with us, he pokes his cheeks and looks at me to ask where she is. Whenever he's away from her, this is what he's doing.