Why is it significant that Holden shows Jane Allie´s baseball mitt?

Showing Jane the baseball mitt was significant because she was the only person he'd ever shown it to.

She was the only one, outside my family, that I ever showed Allie's baseball mitt to, with all the poems written on it. She'd never met Allie or anything, because that was her first summer in Maine--before that, she went to Cape Cod-but I told her quite a lot about him. She was interested in that kind of stuff.

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