Carlo Rizzi felt his whole body go weak with a terrible sickening fear when he saw Michael Corleone standing in his doorway, Michael's face, the face of death

Michael's “You have to answer for Santino, Carlo” made Carlo really sick, physically nauseous

Carlo spoke out of his terrible fear, without dignity, without any kind of pride
Quote
Carlo: Mike, I'm innocent -- I swear on the kids, Mike -- Please, Mike, don't do this to me
Michael: Sit down
Carlo: Mike, don't do this to me, please....

My take, Gianni Russo was very good and pulled off all of the above including his enormous relief! that Carlo's only punishment was only "out of the Family business"

Master manipulator Michael
Quote
Come on. Don't be afraid, Carlo -- Come on, you think I'd make my sister a widow? I'm Godfather to your son, Carlo --