This was from March but it is a good question. It prompted me to do some spot checks on Facebook virality and Twitter virality as well.

One of the things that stands out in false stories is that because they are false they stay "on message" in their falseness. This contrasts with stories that are more truthful which tend to include questions and unknowns that might later contradict or modify the story.

So for an example, a false story about a series of events leading up to an outcome, there are no events mentioned that suggest randomness or any discussion of alternate ways the outcome could have come about. Where as truthful stories have either tests that were done for counter factual narratives or suggestions for other areas that were not covered as completely.

Basically a common theme in truthful stories was they still included "inconvenient" facts which might or might not be significant and the false stories contain no such facts or even hints.

If I still had an ontologist I could talk to I'd try to figure out if we score stories using an ontological structure score (where perfect scoring is most likely false :-).