In The Godfather 2 why does Frankie Pentangeli immediately change his story when he sees his brother?

Question

Frankie Pentangeli is before a committee ready give evidence against Michael Corleone. His brother enters the room and Frankie to immediately changes his story.

Was it just out of guilt or was there another less obvious reason?

Answer 1

There's another less obvious reason that was left out of the final cut of the film.

From Wikipedia:

The finished film leaves unclear exactly what about his brother's presence motivated Frank to change his story. The final film only states that Vincenzo is himself a Mafia chieftain in Sicily. An early draft of the film explains that Vincenzo, shocked that Frankie is about to break his blood oath and betray the Corleones to government authorities, attends the hearing to remind Frankie that he must not break the Mafia's code of silence, Omertà. His brother's presence, as well as the stare they exchanged, serves as a threat that if Frankie follows through with his planned testimony, retribution will be taken against his children, who are living in Sicily under Vincenzo's guardianship.