NThe Big Yellow Bus | Every week a core cast performs a different type of long-form improv with guest improvisers and musicians. At the show I saw the audience suggestion was a place, Antarctica, and every scene was set there. The performers meet once just before going on, which gives a frenetic unpredictability to their bits and leads to prankish pushing and pulling, some of it offstage. It also produces occasional fumbling to discover others' sensibilities and therefore some hesitance and flat dialogue. But two core members are reliable: Lisa Linke's prefaces and narration provide clever direction, and Lauren Lapkus's funny faces, pitch-perfect voices, and black humor are invariably riveting. --Ryan Hubbard a Open run: Thu 8 PM, Playground Theater, 3209 N. Halsted, 773-871-3793, $10, performances free during November and December.