The monsters under Elisa's bed have been getting bolder and bolder. In the morning, when she pulls away the spilled-over covers that had been dragged off the bed, she sees the deep claw marks on her floor.
It's not until another night, when she hears for the first time the whimpers and muffled screams from below, that she realizes that they're not trying to pull her in, but trying to get out themselves.