Immediately after Cassius has a private conversation with Brutus, where he attempts to persuade him into joining the conspirators, Caesar and his followers enter the scene. Caesar proceeds to call Antony to his side and tells him that he prefers to have fat, healthy-looking men around him. He then draws Antony's attention to Cassius and says,
"Yond Cassius has a lean and hungry look. He thinks too much. Such men are dangerous" (Shakespeare, 1.2.195-196).
Caesar's comments reveal that he is an intuitive man, who is relatively cautious and aware of his surroundings. He notices that Cassius has an intense, unsatisfied look on his face, which is both threatening and suspicious. Given the fact that Cassius has just finished venting about Caesar to Brutus and is plotting his assassination, Caesar's words are shockingly accurate and his thoughts regarding Cassius are rational. Unfortunately, Antony tells Caesar not to worry about Cassius and refers to him as a noble, harmless Roman.