In Julius Caesar, Act 2, Scene 1, line 100, what do Cassius and Brutus whisper?
Just before Brutus and Cassius have their little conversation aside, Brutus has asked what the men are doing in his orchard at night - what is it, he asks, rather sardonically, that is keeping them from sleeping:
They are all welcome.
What watchful cares do interpose themselves
Betwixt your eyes and night?
Shall I entreat a word?
Remember that the last time Cassius and Brutus spoke on stage, Brutus was by no means committed to a conspiracy. No agreement had been made. And Cassius has been having people throw letters up to Brutus' window to persuade him. So, somewhere in this little whispered exchange, Brutus signs up to the conspiracy, and agrees that Caesar needs to be murdered for political reasons. Because the next time he speaks, he's sealing it with handshakes:
Give me your hands all over, one by one.
And let us swear our resolution.
We've seen Brutus agonise about the murder and whether it's the right thing to do. This moment has him finally commit himself.