uranium
"Uranium is like a finicky child at a buffet: only the right combination of moderator, fuel, core design and materials will produce a sustained fission reaction."
"An analogy I like better is a mousetrap. Think of the electric force as the spring, and the strong force as the latch. The latch is holding back the spring, and if you pop off the latch then the spring's energy is released.
Then a heavy nucleus like uranium is like a mousetrap with a loose latch: you get a lot more energy out than you put in when you trip the latch."
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.