Last night, I was sitting at the kitchen table with the kids while they ate dinner. Oliver and Hazel were trading made up (and thus, not funny) knock knock jokes and cracking each other up. Henry was staring at them, fascinated, with a half-smile on his face, like he was trying to get the jokes.
They stopped laughing, and Henry looked back and forth between the two of them, and then started laughing. It was really cool to see him learning the social cues and the turn taking of interacting with others.
So I told the kids to start laughing again, and I took a video of it.