Welcome to the Financial Markets Theme Park! That ride with the 250-foot drop over there is Bitcoinesethe stock market. The one with all the twists and turns and loop-the-loops? Those are junk bonds. And that little train that goes around the park? That's the U.S. bond market. Well, until recently.

That slow-plodding train has turned into a rickety roller coaster ride for investors. We head to the theme park to explain.

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