Flavius uses the basest mettle to reveal the worthless spirits among them, and how even the most thickheaded are hard to be emotional touch.
Based on the text, Cassius said "His coward lips did from their color fly", which means that Caesar's lip is slowly fading away its color to reveal his coward personality.
Cassius attempt to justify the conspiracy using fall and falling when instead of saying that Caesar has a disease called epilepsy; a disease where people can be easily fall, but they turned it