لا تعجبي يا سلم من رجل ... ضحك المشيب برأسه فبكى
O Salmā, do not be surprised at a man ... whose greying hair laughed upon his head while he wept.
The laughter and tears belong to different imagined agents: greyness is made to “laugh,” while the person weeps. The pair ḍaḥik and bakā creates a clear semantic contrast, with the first part expressed metaphorically.
The poem does not claim that white hair literally laughs. It creates a scene that joins the onset of age to the person’s grief at its arrival.