He saw something then that terrified him.
: Sealed insulated glass units (IGUs) can crack if transported across significant altitude changes without "breather tubes" to equalize pressure. broken window pane
By evening, the fracture had grown. It wasn't the weather; the day was still. It was something internal—a stress fracture, the experts would say. A structural failure caused by age, expansion, and contraction. But to Arthur, it looked like a decision the window had finally made. He saw something then that terrified him
He looked at the jagged teeth of glass remaining in the sash. They looked like a wound. But the room was no longer stagnant. The smell of damp earth and coming rain replaced the smell of old books and dust. It wasn't the weather; the day was still
It didn't take force. It took surrender.
: Describe it as a sharp crack followed by a tinkling rainfall of glass hitting the floor.