User blog comment:Traffy731/luffy's red hawk attack/@comment-70.185.174.61-20130521142109

When luffy is in gear second, his rubber is already at such an extreme heat that his body creates a steam vapor. When he stretches it to the max and suddenly hardens it to a material harder than steel, the friction that already exists combined with the new friction of a harder-than-steel material stretching and retracting creates an explosive ingition, hence the red hawk.