1.) the opposing leader talk; the argue with those who are on the same side, but they talk to each other ;-)
2.) the two eagles are the omen that bothers Cassius;
"Two mighty eagles fell, and there they perched,
Gorging and feeding from our soldiers' hands,
Who to Philippi here consorted us.
This morning are they fled away and gone,
And in their steads do ravens, crows, and kites
Fly o'er our heads and downward look on us
As we were sickly prey. Their shadows seem
A canopy most fatal, under which
Our army lies, ready to give up the ghost."
3.) They decide that is they lose they will never speak to each other again, but if they ever have the chance to meet again they will do it with a smile.
4.) Brutus sees a weakness in the demeanor of Octavius' men that he thinks can be breached. He was wrong.
"Let them set on at once, for I perceive
But cold demeanor in Octavius' wing,
And sudden push gives them the overthrow.
Ride, ride, Messala. Let them all come down."
5.) Cassius tells Titinius that if he really loves him, he will go to the tents that have been set on fire and see who is there.......... friend or foe; he kills himself because he believes he's sent his friend to his death. This was a mistake because Titinius still lived. Brutus says,
"O Julius Caesar, thou art mighty yet!
Thy spirit walks abroad and turns our swords
In our own proper entrails."
when he sees Cassius' body.