FAQ

They appear to be wearing underwear or at least stockings. So they are likely other actors or background players simply walking to their dressing room.

"The Unexpected Virtue of Ignorance" is the title that the critic Tabitha gives to her review of the opening night of Riggan's play. Before opening night, Tabitha believes that Riggan is ignorant of the art of the theater. But in her review, she considers the unexpected virtue of his ignorance to be the naive-yet-wholehearted, successful performance he gives, including spilling his own blood: "Thompson has unwittingly given birth to a new form, which can only be described as super-realism....The blood that has been sorely missing from the veins of American theater." The meaning of this as a secondary title for the movie itself, or Tabitha's deeper meaning in choosing the title for her review (let alone whether her point of view is sane), is beyond the scope of a FAQ, but could be variously optimistic or pessimistic, in keeping with a movie that is quite open to interpretation. Lastly, the secondary title is potentially an in-joke, stemming from the director and writers' claims that they hadn't made anything this comedic before, and that the movie is rife with all of the artists making fun of themselves.