The Voice tried something new last night – adding a fifth chair to its live, two-hour Top 10 performance show, to let a guest mentor chime in with after-performance reactions. The inaugural mentor for this experiment was Shania Twain, who was very nice, and always had positive things to say. She did not, however, say them quickly enough, or originally enough, to warrant all the air time she gobbled up. But with the right mentor, this might prove to be another welcome addition. On tonight’s elimination show, though, the primary bit of business is to whittle the Top 12 down to the Top 11.