When I was a kid, my parents held the belief that if you keep lily flowers in a vase in a room with the windows closed overnight, and you sleep in that room, you will get a headache. The belief went on to state there is a small chance of death, for the presumed cause that the flowers somehow consume the oxygen in the room. As an adult, I never revisited this superstition; I don't buy flowers often, but my wife does. For some reason, neither one of us ever buys lilies. It could be that we both hold a remnant of this superstition deep inside our subconscious.