Final answer:
Shakespeare uses metaphor and dramatic irony in the messenger's description of Laertes' arrival in Hamlet.
Step-by-step explanation:
The poetic device employed by Shakespeare in the messenger's description of Laertes' arrival in Hamlet (Act IV, Scene V, lines 99-103) is a vivid visual image enhanced by metaphor and dramatic irony. The messenger conveys an urgency and a critical portrayal of Laertes through expressive language. As Laertes arrives, there's a sense of foreboding, and Shakespeare's use of dramatic irony comes into play, as the audience knows more than the characters do about the unfolding events, especially concerning the death of Laertes' father, Polonius.