An error is that the scientist did not control their variables. They had one group of people playing the game at 6, and another group playing at 12. This means that other things might have affected the scores other than what was being tested, which was caffeine.
Plants make their food in their leaves. And need sun for this process, so smaller and fewer leaves means less sun for photosynthesis, and it also means less food to nourish the plant.
