What effect did his appearance at the hearing have on Frank? We know that it caused him to change his mind about selling Micheal out, but why?

Some have suggested that it was because Frank felt ashamed in front of his brother, being seen breaking omerta and betraying old-standing values. Others, more realistically in my opinion, say that Micheal turning up with his brother was understood by Frank as threat that his family will suffer if he continues with his original testimony. The look on his face when he first see's his brother is almost a look of resignation coupled with a look of 'I understand'.


What does everyone else think? Does the book provide any more insight into this situation?