"She heard Harry sigh, and after that they walked in silence for a while, passing through an archway of some reddish metal like copper, into a corridor that was just like the one they'd left except that it was tiled in pentagons instead of squares."

"she was trying to count the number of things in the room for the third time and still not getting the same answer, even though her memory insisted that nothing had been added or removed"

I'm curious though, is there anything in there that would even count as this level of logically impossible? Can anyone remember one?