any idea what specific type of damage caused this to happen to my wife's phone? she used it before bed the other night and it seemed normal and woke up to this in the bottom left corner. touch input still works on the entire screen but the black and blue keeps spreading slowly, despite only using it gently. she was cleaning the kitchen before bed so my thought was she put it too close to a still-hot stove burner, but i'm not sure why the damage would take 12 hours to show up.