At one point, he was sitting on my tummy and he'd gently push me backward, so I obliged and went underwater, blowing bubbles. We did this a couple dozen times, and I'd just calmly come up, get air and go back down again. I could have just bucked off his 'push' no problem, but it seemed a good way to show him that being underwater wasn't a big thing. That it was just a way to be in the water. He just studied me as we did this, quietly and seriously. After all that, though, he grinned big at me, pushed and then stood up on my tummy and started jumping. Hee. I came up laughing.
But it was interesting to see him study the whole phenomenon with other people, too.