to the appropriate miscellaneous page, I think... :)

These are probably proglottids (egg cases) from the tapeworm Dipylidium caninum. They are transmitted to vertebrates when they ingest a flea (such as the ubiquitous Cat Flea) that is infected with the parasite. The proglottids from this species are interesting because they can move for a short time after exiting the body, appearing to be more like individual worms than egg cases until they begin to harden. The proglottids of tapeworm species that are more commonly found in humans don’t have this ability.

I know that the BugGuide doesn’t cover worms (as they are not arthropods), but it might be interesting to include this with the Cat Fleas, since finding these motile proglottids suggests that a Cat Flea was eaten?