backwards and forwards

in both directions alternately; to and fro

來來回回

he paced backwards and forwards nervously.

他緊張地來回踱步。

bend (或 fall 或 lean) over backwards

(informal)make every effort to achieve something, especially to be fair or helpful

(非正式)竭盡全力（尤指為實現(xiàn)公平或給予幫助）

we have bent over backwards to ensure a fair trial for the defendants.

我們竭盡全力保證對被告公平審判。

know something backwards

be entirely familiar with something

了如指掌