Final answer:
Shakespeare elevates the drama of Caesar's assassination through poignant dialogue, notably with Caesar's famous line to Brutus, which heightens the sense of betrayal and amplifies the aftermath emotions.
Step-by-step explanation:
The detail that best demonstrates how Shakespeare uses dialogue to add a dramatic element to Plutarch’s original account of Julius Caesar’s death is the exchange between Caesar and his conspirators. This dramatic staging is exemplified in Caesar’s line, “Et tu, Bruté? — Then fall, Caesar.” His words upon seeing Brutus among his assassins add a profound layer of betrayal and tragedy, which weren’t characterized with such personalized emotion in historical accounts. Shakespeare’s use of concise and emotive dialogue brings the characters and their desperations to life, culminating in the chaotic aftermath expressed through exclamations of “Liberty! Freedom! Tyranny is dead!” by other characters such as Cinna and Cassius, further heightening the dramatic tension of the scene.