Carol is scared by her own reflection in the mirror, but in the next shot of the mirror her reflection isn't visible when she runs past it, nor is the reflection same as the one in previous shot.
Despite being cautioned by the night watchman not to tarry retrieving her watch left in the gallery as it's about to close, she ignores his warning, stopping to unwrap the ice pick she finds attached, needlessly risking being too late and locked in the gallery with the killer.