Ever notice how many songs have lyrics that, while ariose and catchy, sound kinda scary when you actually think about them?
The Beatles "Little Girl" is a prime example. "I'd rather see you dead, Little Girl/ Than see you with another man"...etc. How many times does a song say "I'll never let you go" or "You can't hide from me" or other words to that effect? Fun to sing, but in the real world, you'd be slapping a PPO on that guy in a heartbeat. Think of your favorite love song lyrics and see if they aren't a little over the line, a little obsessive, a little creepy.
Or maybe just being a mystery writer makes me think of things like that.