The addition of a simple birthday balloon makes a scene that was tense enough to begin with in “Brothers” (about a soldier, played by Tobey Maguire, who suspects his wife of having an affair with his black-sheep sibling while he was away in Afghanistan) into that rare sort of dramatic confrontation where the audience dare not breathe until the moment plays out. With all the key characters gathered around the dinner table, younger brother Jake Gyllenhaal brings a floozy to the party. While the clueless guest babbles about herself, one of Maguire’s daughters starts to abuse a balloon, making loud squeaks in a desperate cry for attention. Director Jim Sheridan deftly cuts between the various family members, repeatedly returning to Maguire’s character, who looks ready to stab someone with his silverware. As others try to intervene, demanding the young girl stop playing with the balloon, she blurts out the worst possible lie.