'A WEASEL IS wild. Who knows what he thinks? He sleeps in his underground den, his trail draped over his nose." With these opening sentences, Annie Dillard starts the essay that Anne Bluethenthal gave to choreographer friends Kim Epifano, Krissy Keefer, Mercy Sidbury, and Susan Van Pelt, asking each of them to create a solo for her. In her own works Bluethenthal – who with this concert, "Living like Weasels," named after the Dillard essay, celebrates the 20th anniversary of her Anne Bluethenthal and Dancers company – has always been interested in examining what is below the surface. Even the titles of her pieces, such as Excavations of the Spirit (from which she will perform her signature solo, In My Bones, for this program) and Tears of Rock, are testimony to the fact that for Bluethenthal, dance is a way to make visible what is ordinarily unseen. While her choreography is crafted to a very personal perspective, for this performance she entrusts herself to artists with different formal propensities; they may bring something out in her that not even she has been aware of. Fri.-Sat., 8 p.m.; Sun., 6 p.m., 3316 24th St., S.F. $16-$18. (415) 273-4633. (Rita Felciano)