Casca is upset over the storm and reacts emotionally to it. He is "breathless" and "stares" as if he were frightened. He describes the storm as a "tempest dropping fire," and says he has never seen such a thing before. He believes it either a sign of trouble in heaven or that earth has become "too saucy" and provoked the gods. Although Casca interprets it and other strange signs he has seen as supernatural omens, he does not try to guess what they foretell. He merely says:
When these prodigies Do so conjointly meet, let not men say, “These are their reasons. They are natural."
Cassius also understands the storm as a supernatural warning from heaven that something "monstrous" is about to occur but claims to know exactly what the monstrous event is. He persuades Casca that the problem is the upcoming proclamation of Caesar as emperor and says they have to stand up against him or become slaves. He recruits Casca into the anti-Casar conspiracy. In other words, Cassius interprets the storm to suit his own political agenda, something Cicero had just warned Casca against when he said:
But men may construe things after their fashion, Clean from the purpose of the things themselves.