What's this about?

Walking beside a different river this evening - the river Tay flowing through Perth (Scotland, not Western Australia!) I'm just here for tonight then home again tomorrow. I was going to add some extras of close ups of this, but the iPad doesn't want to know. There was a poem in Scots on the pillar which presumably explains the sculpture but all I could nearly understand was something about not lying or the snails will get their horns out !? Perhaps I'll find someone tomorrow who can explain.