Carlo was smirking and thanked Papa, truly believing he has fooled the Corleones
Nothing like having a right-hand man spy, who Set up Sonny to be killed, feeding Barzini all the inside information
(At Connie's wedding):
TOM
Now your new son-in-law; give him something important?
VITO CORLEONE
Never. Give him a living, but never discuss the Family business with him.