It’s been raining. No problem with that (must wear the shoes without large holes in the soles next time, though), but in the centre of Leeds – and especially on my route to work and outside the buiding – we have some loose flagstones.
Well, they’re more like paving stones, but you get the idea.
Anyway: to save money (one assumes), to level out the loose ones, they are hoiked up and a sand mixture is placed underneath. The flags are then tamped down level with the rest.
Of course, once it starts raining, the sand becomes mushy. Sand does that, when it gets wet. The flags then become unbalanced, trapping water underneath; so that, if you stand on one just wrongly, your shoes and trouser bottoms get covered in a sand and water mixture that isn’t going to simply wipe off.
All you can really do is put your head down and either miss them entirely or make sure you step square in the middle of them. You’ll know which are loose by the splash marks from previous victims…