I always get songs stuck in my head, often for days at a time. While it's common in the general population, I KNOW that mine is more frequent and more severe. I know it's part of my OCD, because the song repeats without end and does so in the back of my mind. I can be talking or reading or doing some other task, and the song is playing in the background. Another reason I know my "earworms" are OCD is because, without fail, if I get stuck on a new song, it's because the verse that I find the most catchy has seven syllables. Whenever I get obsessed with a new song, especially one specific part that plays over and over again, I'll count the syllables, and sure enough, it will have seven. For example, I recently became stuck on the N'Sync song "Dirty Pop", and the part that I hear over and over is the line, "or the ice around my neck." Count the syllables- there are seven! 
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Helinger: Now, what do you see, John?
Nash: Recognition...
Helinger: Well, try seeing accomplishment!
Nash: Is there a difference?