What does the poet suggest about the ‘relationship’ between the poet and the girl in the first four lines of the last stanza? How does the patterning of words contribute to this?

    Only when the train heaved noisily, only
when it jolted, when it slid away, only then,
daring and secure, she smiled back at my smile,
and I, daring and secure, waved back at her waving.
And so it was, all the way down the hurrying platform
as the train gathered atrocious speed
towards Oxfordshire or Gloucestershire.

Who smiles first?
Who waves first?
Can you be daring and secure?