Certainly they do, when they are moving. But knowing how a nutcracker works gives you no insight as to how it is made. You can compare it to other devices similar to nutcrackers, and you can explain the physics of how it works, but you have no description of how it is made.
What a fatuous statement. Knowing how it works tells you quite a lot about how it's made. Knowing it cracks nuts requires it be made of something of a certain hardness. Observing it works by leverage tells you it is designed using an underlying principle. Observing its finish tells you what manner of tool was used to make it. Etc....