Thank-you for shopping

Always nice to be thanked for the functional. I think I should have offered thanks in return, something along the lines of 'thank-you for being a five minute walk away and being therefore the supermarket I use most.' I shall do so next time, promise.

I'm intrigued though by the sign about the trolley. Does it really stop? It's the 'flask question' - how does it know? How does the flask know it shouldn't make your hot drink cold? How does the trolley know? Is it infra-red? Is there a guard on watch? Is it more simple than I'm thinking? These things trouble me, so I'd better go and chat to Google. And I shall say thank-you afterwards.