Inspired by this recent question.
If, sometime shortly before writing was invented, some passing alien turned the moon into a tiny black hole (xkcd) when/how/would we have figured out it was there, and what it was?
Given it's tiny cross section it is not likely to be eating much and thus would not be very bright. I'm sure people would have been puzzling for quite some time about what causes the tides but I doubt they would figure it out just from that. Sooner or later astronomers would notice that the earth wobbles in it's orbit. Would that be the first good clue that something is there?
