I'm not sure if everyone expiriences this, but I've always known that my thoughts tend to move at astronomical rates. I can recall basically every scene in an entire movie in a few seconds or go over every second of a driving route in my mind, looking at all the houses and landmarks along the way, and get there in my head faster than humanly possible.
This can really mess up word association games, especially if you like to take mental two/three-steps-at-a-time like I do. In a split second, I can go from balloon to the Stanley cup (balloon->hot air balloon->Jules Verne->Around the world in 80 days->Jackie Chan movie->Jackie is inspired by Charlie Chaplin->Charlie Chaplin's moustache->playoff beard->playoff Hockey->Stanley Cup), but it's fun to do and it's great for things like math and chess as you're able to consider multiple paths at the same time.
I was thinking about this the other day when I was driving home from work. You see, I normally go under a tunnel on my way home, so the radio would go static for about 30 seconds. If there is a song playing at the time, I would usually try singing along in my head and see if I can come out of the tunnel on beat with the music.
However, no matter how hard I try to keep with the tempo, I always seem to end up about 5 seconds faster than the song. I guess that's just the nature of things.