My friend found this slip of paper in the vents of his house in NE Portland, an apparent relic from its previous residents. On the front is a child playing with an adding machine. On the opposite side, a child has written “I will eat you.”
This is what I imagine regarding its origin: the child who wrote “I will eat you” had a little brother or sister who believed that there’s a monster (or a dragon) living in the vents. He/she writes “I will eat you” on the back of the paper and slips it down into the vent, believing that eventually, the note will fly out and be discovered by their sibling. The sibling will come to the logical conclusion: the monster knows I’m here, and it will eat me.