The beginnings of an animosity between the two dated back to when they starred together in the film No One Killed Jessica. Vidya Balan made it to the nominations in the leading actress category while Rani was given a nomination in the supporting actress one. This infuriated Rani and she didn't attend the awards. Vidya had picked up the award on her behalf.
So recently when Vidya was asked for the actress with the most fake smile, she named Rani Mukherjee. That's a Grrrr, instead of a Prrrr!