As it turns out, the patron who barfed informed my coworker about the incident after she got motion sickness from the microfilm whirring by. I'd heard about microfilm-use based illness, but this was the first time I'd witnessed the, er, by-product.
So kids, when you fast-forward microfilm, look away! Your gastric health might depend on it!
when I become a librarian stand-up comedian, this is going in my routine.