Shopping for Granny
You arrive at the shop. It was a pleasant journey; short enough to enjoy it, but long enough to prefer not to repeat it unnecessarily. The bell rings as you open the door, and you are greeted by the warm weathered smile of the shopkeeper.
"Good morning! Come to do some shopping for Granny, have you?"
"Yes, sir," you respond politely.
"Well, what can I get for you?" he asks.
"Thirteen items," you recall Granny say before sending you out the door with your overcoat buttoned up just so. "It is very important that you remember them all."
You listened intently as she named each one, taking care to imprint it in your mind. As you walked to the shop, you carried your mental list in your finest metaphorical pail, taking care not to spill a drop. Upon facing the shopkeeper, however, you suddenly find that your pail had been swapped for a colander.
You look on the floor behind you, half expecting to see a puddle or a trail of water. Alas, nothing is left behind of Granny's list.
You suppose you'll just have to guess.