In Act 4, Scene 2, Lucilius confides in Brutus that Cassius's behavior is becoming untrustworthy. Brutus suspects his shifting loyalty as well, and uses simile and alliteration to articulate his suspicions:
Thou hast described
A hot friend cooling. Ever note, Lucilius,
It useth an enforcèd ceremony.
There are no tricks in plain and simple faith;
But hollow men, like horses hot at hand,
Make gallant show and promise of their
Brutus makes a simile comparison between his “hollow,” or insincere, men and over-eager horses that are difficult to handle when first mounted. His point is that Cassius (the "hot friend cooling") lacks sincerity; the force of his simile is powered by the connection of alliterated /h/ sounds across Brutus's dialogue: /h/ast... /h/ot... /h/ollow men, like /h/orses /h/ot at /h/and.
Shakespeare is a legendary wordsmith, and he crafts his sentences for their sonic effect just as much as for their meaning. This passage is a prime example of how he layers literary devices to render them more vivid for the audience. Julius Caesar presents a lengthy investigation into the power of language in speech to affect political change and sentiments, and every line of dialogue presents a point of departure for this exploration.
Over the course of the play, authenticity emerges as crucial character trait for anyone hoping to emerge as honorable—even as various political players in Rome prefer to cling to a destructive sense of masculinity. As Cassius reveals himself to be a particularly duplicitous character, his inauthenticity comes into conflict with Brutus's sense of honor.