Each section introduces an item (a toy) that you can use to solve puzzles. But at some point to get deeper into that section, it requires a second toy from a different section. E.g. the seahorse section introduces the bubble blower, but to finish that section you also need the disc. The chameleon section introduces the slinky, but to finish it you also need the yo-yo. The ostrich section introduces the yo-yo, but to finish it you also need the bubble blower.