Since long before there was any such thing as a "mashup," I've had an innate (and might I say impressive) ability to take two songs, often of disparate styles or eras—and get them totally confused. Or, if you will, mashed up. Considering that so many songs share time signatures, tempos, keys, chord progressions, etc., that's not terribly surprising, but I didn't know anything about any of those things when this started.
For example, when I was a young lad, I was convinced that I had come up with the greatest melody of all time. Some time later, I realized it was basically the chorus of "Born to Be Wild," crossed somehow with Tommy James' "Crimson and Clover." I've never been able to reproduce that melody on an instrument, or even hum it. I just know it was there, in my mind, and it was in essence (if not in form) what we now call a mashup, only somehow even more warped.
This kind of musical synesthesia still happens to me from time to time. Most recently, part of an Apollo Up! song got lodged in my head, as songs will. I couldn't even remember what song it was, or the lyrics, but this one section of the song kept repeating, and I couldn't shake it. A couple days later, same song, same effect. A couple days after that, I got Paramore's "Misery Business" stuck in my head, for whatever reason. (I hadn't heard the song in months, that I remembered, unless Brad played it at The End a couple weeks ago between bands.) I'm sure you see where this is going.

