Lonergan, a playwright, has a great ear for the way real people interact, and he knows how to shape scenes that lodge indelibly in your memory. The characters he creates–who include Sammy’s lonely 8-year-old son, Rudy (Rory Culkin), who idolizes his childlike uncle, and Sammy’s annoyingly fastidious new boss at the bank (Matthew Broderick)–all have the ability to take us by surprise. None more so than Sammy, whose capacity for running amok can rival her brother’s. It’s rare these days that you encounter movie writing this deliciously perceptive. Linney is wonderful: a proper, porcelain teakettle brimming over with newfound steam. Ruffalo manages to be simultaneously hilarious and poignant. Lonergan himself appears in several slyly funny scenes as Sammy’s up-to-date priest, in whom she confides her sexual misadventures. This seriocomic movie may look modest, but it has a surprising emotional undertow. Few films have explored the complicated bonds of love and resentment between brother and sister with such delightful honesty.