Think of a enzyme as a glove and its substrate as a baseball. They are made for each other. One captures the other. Now think about a baseball glove with a large softball in it. The glove can no longer effectively capture the baseball because there is another ball blocking the pocket. It much more complicated than this, but the essence is something is blocking something else.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.