Not to be the party pooper, and admittedly I don't know the context of this statement in the Acts of Thomas, but knowning that it comes from a Gnostic text, it sounds an aweful lot like a Gnostic metaphor, possibly for the moment of realization of the great knowledge of Gnostism. It seems like something that might refer to the moment in time where a person with the spark of knowledge realizes the evil and vapidness of the natural world.
Just a thought.
No party pooper... just discussing. It very well could be Gnostic metaphore... but then it does seem to refer to a shroud with a mirror image on it, if you accept that translation.