The word "swinging" in the second sentence not only indicates that the poet is swinging in the stream, but also indicates that the poet is in a happy mood.
More importantly, Xie Zi described the scene when the poet often built ships under the Yanglin forest in Dongdutou, and the rain turned from fine to thin and finally stopped. Swing characters describe the boat that carries the poet to his friend's seclusion. The water waves ripple and the boat swings slightly.
"Two words" endow this poem with a dynamic aesthetic feeling, which is no longer a static picture, but a coherent picture.