Tomorrow, they're making models of early communications about trade from modelling clay. Basically, that paranoid herder decided to make one little clay ball for each animal and encase the balls inside one bigger ball, which he then baked to harden it. The second farmer broke the ball and counted the little pellets to find out how many head of cattle had been sent. The progression to writing from that point was not too difficult.

If the ancient nomads of North America had decided on clay balls instead of smoke signals, civilization would have developed here first. :) Still, it would be a good solution. The problem had them talking all day.