Dead Silence (2007)

Jamie Ashen: Who would've dug up a dummy and sent it to me?
Henry Walker: I don't know! No one from this town dares speak Mary Shaw's name, let alone go near her grave. They know she won't stop killing, until the screaming does.

Trivia: The making of the film was a troubling experience for writer Leigh Whannell and director James Wan. The story was created at the last minute for a pitch to studio executives who wanted to hear something from the "'Saw' guys" (even though they had no concrete ideas at the time), but after the project was greenlit, Whannell found it difficult to write as he was not fully passionate about the project and didn't expect them to give the go-ahead to make it. Upon completing the first draft, he then spent well over a year doing copious re-writes over and over to appease various increasingly harsh notes the studio gave him, including notes he felt made no sense. (Ex. The executives in charge kept pushing him to create "rules" to make the story more grounded and realistic even though it was a story about an abstract ghostly curse.) Eventually, an uncredited script-doctor was brought in to re-write the film, and Whannell has stated that the finished film is a mish-mash of his ideas and the script-doctor's. The shoot ended up being hectic and troubling for director Wan, and a great deal of content was cut from the film, including a good deal of the twist finale and a good deal of the backstory related to the various villains. Whannell has said that although the project was a failure in his eyes, he would do it all over again because it taught him many valuable lessons about filmmaking.

Question: Why did Mary get angry when the boy in the audience said that he could see her mouth moving? When a close-up of Mary is shown, she's moving her mouth.