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.

No cockroach could ever be allowed to set spiky foot in there.

Skeptics have pointed to the limits of Friedman s metaphor. As one put it, the world is not flat, but spiky.

But the interesting thing about these computer virus infections was that, if you look at the rate at which the infection worked, they show this spiky behavior that you're used to from a flu virus.