Shape Sorters

I was sitting outside a coffee shop in Shoreditch people watching and waiting for a Blip opportunity. Missed the bloke in a shaggy Afghan sheepskin coat and a huge Great Dane. And the bloke on a bike with an aspidistra in a pannier. 

But then this woman walked across with the hard box on her back (that's a large violin - ha ha - bet she's only heard that one a million times). It occurred to me that the shape together with the bin slot was a bit like a children's shape sorter game.