Thanks! The worms and book stacks are completely randomly generated - so sometimes it's just the luck of the draw. That one odd worm must have been a leftover from when I was experimenting with them.
Earlier on in the jam, the game generated 100 worms (some higher up on the shelves), most of whom were silent and well behaved residents of the library, and you were only supposed to grab them when they were making noise (they started/stopped making noise on an random basis when left to themselves). Grabbing any of the silent ones would cause it to make noise, and cause nearby other silent worms to make noise. Bumping into walls or floors while carrying the worm would cause you to drop the worm.
The only problem is that I couldn't figure out a victory condition for the game, so I dumbed it down to this current "find 12" state in the last few panicked minutes that I had available during the jam before I had to head out for a previous engagement.