The Dream Nail in Hollow Knight is presented as a tool for entering dreams and cutting through memory — its primary function in the main quest is accessing dream bosses and progressing certain NPC questlines. Its secondary function, available from the moment you acquire it, is reading the thoughts of every living being in Hallownest. Almost no one is required to do this.
Grubs trapped in jars think about light and warmth. Moss creatures in Greenpath experience time on a scale where decades feel like moments. The Dung Defender — one of the most enthusiastic NPCs in the game — has interior thoughts of deep loneliness in the moments between his boundless external energy. Quirrel’s thoughts throughout his questline chart an arc of purpose and peace that his dialogue only partially reveals.
The most significant Dream Nail interaction: at the end of Quirrel’s questline, you find him sitting by a pool at the Blue Lake — peaceful, facing the water. Dream Nailing him reveals a thought that indicates he has found what he was looking for and is at rest. Returning to the Blue Lake after a long absence finds him gone. Only the Dream Nail interaction explains what his disappearance means.
Team Cherry gave interiority to every creature in the game — not just the story-relevant ones. Wandering enemies have thoughts. Background creatures that never interact with gameplay have inner lives. The world is presented as fully inhabited in a way that most games approximate and Hollow Knight actually builds.
Found this by accident on my third run. Came here to understand what I was actually looking at. Great write-up.
Saved this article for my gaming reference folder. Essential reading for anyone serious about this game.