things that are stuck in my head

Why are these things stuck in my head? They pop out all the time, and I can’t for the life of me figure out why.

• The Bilestoad - a game for the Apple ][e. Playing this game looks like piloting shrimp competitively.
• Captain Midnight - I started singing the theme from this game about two days ago. But why?
• that other western shootout game whose name I can’t even remember but whose theme song is stuck in my head forever.