According to Mary, what circumstances allowed her to pretend in court, but not in the vestry?
Mary Warren fails to convincingly expose the fraud of the witch trials in The Crucible when she is asked to faint after saying that her earlier fainting spells had been fake.
Danforth pushes Mary Warren to prove that she was faking her fainting by doing it again, but she says she cannot. Though Mary Warren repeatedly insists and says she only thought she saw spirits, she cannot summon the guile or the emotion to perform in front of the group and faint.
The reason she cannot faint in court, she says, is that she has no "sense of it now". When she had been going along with the other girls she "thought" she saw spirits because all the other girls saw them.
"It were only sport in the beginning, sir, but then the whole world cried spirits, spirits, and I - I promise you, Mr. Danforth, I only thought I saw them but I did not."
Without a sense that she is participating in the mania of the group, Mary Warren cannot faint or see spirits. She is not caught up in the group's fantasy. Abigail's genuis for manipulation soon brings Mary Warren's argument crashing down as Abigail concocts a new scenario, pointing to a spirit on the ceiling and giving Mary Warren one last chance to recant her testimony.
Abigail's ploy works and soon Mary Warren is seeing spirits again and blames it on John Proctor.
Mary Warren's claim is very close to the truth here as she argues that she loses her "sense" of the fraud when she is separated from the group. She quickly regains this sense by rejoining the group headed by Abigail.