I should know better

On the way back from a local show where Tess Trueheart singularly failed to distinguish herself and I picked up a lot of gossip, I called in at the big Tesco to shop.  Plastic bags are forbidden now, in the name of Saving The Planet, so i produced two canvas ones when  the checkout girl kindly offered to pack for me.

They were soon filled, and I reached into a pocket and pulled out the big string

 bag. 

She looked at it lying there, like the discarded skin of some exotic animal.

“What is it?.   What does it do?”

I explained, reasonably, that it was a string bag.

“You mean things go inside it?   How does it work?   Where do things go?”

I kept a straight face as I pointed out the opening, and the handles, which pretty well exhausted this branch of string theory.  She continued to be loudly amazed at the amount it held.
I lugged home the sagging bag, also amazed that

a)  at my time of life I had gone back to using string bags, which up to now had been a vague childhood memory
b)  I should have to explain this strange technology to a teenager.   Or indeed anyone.