From Elie Assis, Chiasmus in Biblical Narrative: Rhetoric of characterisation, Prooftexts, Volume 22, Number 3, 2002, pp. 273-304
A. 18 And he (David) said, Wherefore doth my lord thus pursue after his servant? for what have I done? or what evil is in mine hand?
B. 19 Now therefore, I pray thee, let my lord the king hear the words of his servant.
C. If the LORD have stirred thee up against me, let him accept an offering:
C’. but if they be the children of men, cursed be they before the Lord; for they have driven me out this day from abiding in the inheritance of the LORD, saying, Go, serve other gods.
B’. 20 Now therefore, let not my blood fall to the earth before the face of the LORD:
A’. for the king of Israel is come out to seek a flea, as when one doth hunt a partridge in the mountains.