It was Joey Hart, one of Mr. Martin's two assistants, who had explained what the gibberish meant. "She must be a Dodger fan," he had said. "Red Barber announces the Dodger games over the radio and he uses those expressions — picked 'em up down South." Joey had gone on to explain one or two. "Tearing up the pea patch" meant going on a rampage; "sitting in the catbird seat" means sitting pretty, like a batter with three balls and no strikes on him.
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What does picked 'em up down South mean and why is a dash used before it?