Have you heard the one about the timid professor and the sexpot student? At first this familiar scenario is key to director Terry Domschke's interpretation of Eugene Ionesco's classroom classic, and it works quite well: Katie Korby as the seductive pupil, Joseph Schuman as the mousy academic, and Sylvia Grady as his matriarchal housekeeper establish spellbinding verbal and physical harmonies. Then Domschke appears to lose conviction and this Janus Theatre production veers suddenly from modern consciousness to introduce a hackneyed image rooted in the play's 1951 premiere--an image that lets the audience off the hook. By the end of the evening, when the professor reminds us that "we can't be sure of anything in this world," we're forced to concur. Through 1/23: Thu-Sat 8 PM, Sun 7 PM. Athenaeum Theatre, first-floor studio theater, 2936 N. Southport, 312-902-1500. $12-$15.