Milo began to think as hard as he could (which was very difficult, since he wasn't used to it). He thought of birds that swim and fish that fly. He thought of yesterday's lunch and tomorrow's dinner. He thought of words that began with J and numbers that end in 3. And, as he thought, the wheels began to turn. "We're moving, we're moving," he shouted happily. "Keep thinking," scolded the watchdog. —The Phantom Tollbooth, Norton Juster In this passage, the word wheels has a literal meaning and an idiomatic meaning. Explain how the meanings differ.