Wasp eater/Mad

Creator
Although it would apparently make little difference to the plot, it seems to be the case that the weasels were created some time in the past and only recently repurposed as revenant detectors. There actually is a known candidate for their creator, then: the former spark who worked (and to a certain degree still does work) in small, furry animals; namely, Dr. Dimitri Vapnoople

Which could lead to one or more other mad theories.