In the intermission for Tosca live from the Met in HD was a short look at a piano rehearsal for Falstaff which will simulcast on my birthday. They were rehearsing the end of Act II where Falstaff is thrown into the Thames in a laundry basket. Angela Meade is Alice Ford, Lisette Oropesa is Nanetta and Stephanie Blythe is Mistress Quickly.
James Levine was conducting in his automated chair, but next to him was a white-haired woman with a score on a music stand making gestures that at times resembled conducting. Levine conducted all the time in the way one is accustomed to seeing, but the woman seemed only to conduct the singers. She would hold up her hand with the palm toward the singer, and when it came time for the entrance, she would point at them. I am revealing the incredible limitations of my professional experience when I say that it took me a minute to figure this out. This person can only be the prompter.
When I sang in a professional theater, there was a prompter in the wings who only spoke the words just prior to when the singer sang them, usually not loud enough to be heard. The woman in the film today never seemed to say anything. Levine ignored her.