Brutus very magnanimously gives Antony permission to deliver the main oration at Caesar's funeral. Cassius, who is far more practical and worldly wise than Brutus, warns his partner that this could be a very serious mistake. He says:
You know not what you do. Do not consent
That Antony speak in his funeral.
Know you how much the people may be moved
By that which he will utter?
But Brutus' only fault is that he is infatuated with his own nobility and benevolence. He tells Cassius:
By your pardon,
I will myself into the pulpit first,
And show the reason for our Caesar's death.
What Antony shall speak I will protest
He speaks by leave and by permission;
And that we are contented Caesar shall
Have all true rites and lawful ceremonies,
It shall advantage more than do us wrong.
Brutus' speech is logical but it seems stilted and lacking in feeling. Antony's, by contrast, is spontaneous, natural and democratic, full of emotional appeals--and Brutus did not know that Antony had an "ace in the hole" when he asked permission to give a funeral speech. Antony is concealing Caesar's will in his tunic, and he uses this at the last moment to sway the crowd. Brutus and Cassius are forced to flee the city because the Roman people are burning, killing, and looting. They are looking for any member of the group who plotted to assassinate Caesar, and they are so incensed that they murder a poet who just happens to have the same name as one of the conspirators.
Much later during a parley on the battlefield at Philippi, Cassius tells Antony:
The posture of your blows are yet unknown;
But for your words, they rob the Hybla bees,
And leave them honeyless.
True to his character, Cassius is flattering his enemy with the hope that it might do him some good. He is possibly hinting that he might be persuaded to betray Brutus and come over to the other side even at this eleventh hour, or possibly hoping that his life might be spared if Antony and Octavius win the coming battle, as Cassius has good reason to think they will. He is also taking a subtle dig at Brutus, reminding him of how thoroughly Antony bested him in their oratorical contest on that crucial day, the Ides of March, in Rome.
They somehow get to know that Antony has incited the mob in his speech, and escape, on horses, from the gates of Rome "riding like madmen".