You are stuck in a cement room with no windows or doors. There is no light. The only things on the room with you are a table and a mirror. How do you get out?
In the mirror, you will notice the dark ρá†ch, and using the table wood, you can break the wall and escape.
A cement wall doesn't mean that the wall is wet or dry. You happen to notice the dark ρá†ch on the wall where the cement was wet, and thus if you push the wall using the table wood, it would break easily. Thus you can escape easily from the room.