True story, I believe: a married couple, both child psychologists, had one of their grad students visiting them at home, and the student decided to do some impromptu experiments with their youngest kid. Sits on the floor, plays, asks “Which of these containers do you think there’s more in?” (Classic demonstration of “conservation” - that kids under a certain age don’t recognise that the same volume of stuff IS the same if it’s poured into a different shaped container.)
The kid points to one. “That one.” Looks the grad student in the eye. “But you shoud ask my brother, Henry - he’s got conservation already.”
