The Hollow represents the loneliness of people, that sometimes haunt us. When there are certain times that people are not able to share what they want to say, hiding what they do or who they are. The Hollow is the human shell, the form without a soul for a few minutes.

Glaring at the silent moon at night, without a sound; only movements will be the dark clouds that swarm across the lonely skies.
Too soon does night approach, until we live a life in emptiness, silent and Hollow.

Do what you have in heart, or your soul will leave you.