Certain theatrical productions could benefit from audience recognition that the show is about them.
The idea is to rig a continuous sheet of "one way mirror" material at an angle such that when illuminated from the stage, it is transparent to the audience.
At a dramatically appropriate moment,
the lighting reverses: the stage becomes dark, and the house lighting allows the audience to view themselves in the thusly-created mirror.
Possible refinements include warping of the mirror by vacuum / pressure for "fun house" effects, or spotlight accentuation of audience members.