The title stems from the term "mirror twins", used to describe Patricia and Cheryl Davenport in the episode. The full term "mirror image twins" describes twins who exhibit characteristics with reversed asymmetry, such as dominant handedness or organs, just as the Davenport twins were described.
Despite being credited in the opening sequence, A.J. Cook, who portrays JJ, doesn't appear in the episode. This is the 1st of 29 episodes in which characters are credited despite not appearing in the episodes.