Conor McGregor whispered some words of psychological warfare to Floyd Mayweather during their final face off on Wednesday ... and now we know exactly what he said. 

Take a look ... Conor leans in and takes a few quiet, private shots at Floyd. 

Floyd responds, "You're a comedian."

Despite the trash talk -- the two men exchange final pleasantries ... quietly wishing each other good luck. 

And get this ... the UFC has released new footage from Conor's sparring sessions with Paulie Malignaggi showing the Irish superstar putting a beating on the former champ. 

Paulie is now saying he was spying for Floyd the entire time. Hard to spy from the canvas though. 

NEW SPARRING FOOTAGE