While walking back after the festivities of Lupercal, Caesar and Antony talk about Cassius. Caesar doesn't trust Cassius because he believes he has too much negativity, but Antony denies those claims.
Yond Cassius has a lean and hungry look, he thinks too much: such men are dangerous.
Fear him not, Caesar, he's not dangerous,
Cassius and Brutus ask Casca about the cheering at the festival of Lupercal. Casca reveals that the cheering was because Antony offered the crown to Caesar 3 times, but Caesar denied each time.
I saw Mark Antony offer him a crown-yet 'twas not a crown neither, 'twas once; of these cornets--
While talking about the festivities Casca reveals that Caesar had a seizure during the festivities. After the seizure Caesar doesn't want to show any weakness to his people, to show bravery Caesar opens up his shirt and offers his throat to cut.
He plucked me ope his doublet and offered them his throat to cut.
He fell down in the market-place, and foamed at mouth, and was speechless
After Brutus leaves, Cassius reveals his true plans to the audience. Cassius plans to throw letters, that will praise Brutus, at his window. He hopes this will convince Brutus to become king, so Caesar is not king anymore.
I will this night In several hands, in at his window throw, as if they came from several citizens,