Mind of a Mine?

• We were driving and talking. We were talking about the mind. I don't recall why.
• Mica's into defining things, which is good because it's building his vocabulary.
• Mica said, "The mind is when trains roll down the track, and go into the mind. It's also in your head."
• We were like, "What?" 
• Mica said, "You know like in Thomas when the trains go to the mind."
• He was talking about a mine.