A return visit to the Scrabo school site, involving much rummaging under bushes and behind rocks, uncovered a can formerly containing 'Wacky String' which presumably was a rival to 'Silly String'. A relic of the last days of the school, perhaps? The manufacturer still exists.
My capable assistant is indicating a very small slug, in case you missed it.
We also discovered the rusted metal frame of a classroom chair ( inverted ), which did not seem to appeal to slugs.