I felt that FFC provided us with a buildup. Notwithstanding his cowardly behavior, Carlo still had a measure of "pride." Following his beating and public humiliation by Sonny, and Sonny's putdown of him at the dinner table after the Don returned from the hospital, we might have expected that Carlo would be thirsting for revenge.
But the clincher came when Sonny was ambushed on the causeway. How did a carload of guys armed with submachine guns, and a toll-taker who was in cahoots with them, know exactly when Sonny was going to get on the causeway? Was it a coincidence that he leaped into his car after Connie called the mall following her latest beating by Carlo? So, when Michael said, "You have to answer for Santino, Carlo," it didn't come as a surprise to me. And it didn't come as a surparise that he was garrotted instead of being taken to the airport. If Michael didn't give old-timer Tessio a pass, he sure wasn't going to let Carlo off the hook.