An Unexpected Result

This term, the students in my third-year software engineering course have been working in teams to build a shared to-do list plugin for Facebook. Each of the six teams has worked independently (well, as independently as students ever work) for the first three exercises. For the fourth, each team conducted a review of every other team's code to decide which one they would continue with for the final exercise. They had to switch: teams were not allowed to continue with their own code. Dave Wortman has been doing this "review and buy" exercise for a couple of decades. This time, the result is almost a perfect permutation:
  • Cereal and Pancakes have bought Waffles.
  • Eggs has bought Fruitbar.
  • Fruitbar has bought Cereal.
  • Porridge has bought Eggs.
  • Waffles has bought Pancakes.
I was surprised, as I'd been expecting there to be a clear winner. I'll be reviewing (and grading) the reviews over the next few days; it'll be interesting to see whether groups got different answers because they're using different criteria, or because... um... hm, I don't have another hypothesis just yet.