One of them is Kiki, one of them is Buba.

Which one is Kiki and which one is Buba?

How many of you think that's Kiki and that's Buba? Raise your hands.

How many of you think that's Buba, that's Kiki? Raise your hands.

He had to fetch flowers, ten times a day, from the Mont Popa, few dozens of miles away from Bagan.

Because we instinctively find, or create, a pattern between the round shape and the round sound of Bouba, and the spiky shape and the spiky sound of Kiki.

It's a primitive form of abstraction, and we now know this happens in the fusiform gyrus of the brain, because when that's damaged, these people lose the ability to engage in Buba Kiki, but they also lose the ability to engage in metaphor.