دَخَلَ زَيْدٌ وَهُوَ مُبْتَسِمٌ.
Zayd entered while smiling.
On a circumstantial reading, wa-huwa mubtasimun describes Zayd’s condition during the entrance; the pronoun refers back to the bearer of the circumstance, while wāw helps mark the link. A different context may support a distinct predicative reading.
A circumstantial clause chiefly qualifies an event, rather than adding another independent report. The decision between ḥāl and coordination therefore depends on grammatical relationship and discourse meaning, not merely on finding the letter wāw.