In a 1988 interview, Frank Black gave this explanation of his songwriting process:
"Eighty percent of it's baloney, yeah... I write the songs by singing a whole bunch of syllables along with the chord progressions, and they become words. A bunch of five words might mean something, or stand for something. But the five words after it, or preceding it, sure as hell won't have anything to do with them."
It seems that the point of Pixies lyrics is not to get at specific meanings or themes, or even to follow a steady structure. For example, even though Black talks about singing "syllables along with the chord progressions," those syllables don't usually end up matching from verse to verse. Take how the second line of the first verse, "try this trick and spin it, yeah," is only seven syllables, while the second line of the second verse, "animals were hiding behind the rock," is ten. The two lines have almost the same melody, but are still structurally unique. This affects how they are sung, and contributes to the idiosyncratic vocal style Black is known for.
We here at Shmoop like some ambiguity in works of literature and music, but sometimes a work doesn’t even have a couple of competing analyses—it's just plain hard to figure out. We think that's the case with "Where Is My Mind?". Maybe we should just approach Frank Black's does art the same way he did: "It's definitely arbitrary, about going with the immediate...about saying something without thinking about why you said it, and because it has a root inside you, it's much more real, true to you, than if you think and analyze everything."
We can't resist pointing out, though, that since Black can tell you why he prefers to write the way he does, he has probably—consciously or subconsciously—analyzed other ways of writing and rejected them in favor of his own.