Back in the Middle Ages, when a noble transferred title to land it was a common practice to have one or more children witness the transfer and then someone would slap or hit the children. It was believed, probably correctly, that the kids would be prone to remember the day that So-And-So slapped them upside the head, thus linking the memory of the slap to the memory of the transfer of the title to the land, i.e. for most of his life the kid would be a witness to the event.
Here is a quote from Wikipedia about the “Livery of seisin”:
“The oldest forms of common law provided that a valid conveyance of a feudal tenure in land required physical transfer by the transferor to the transferee in the presence of witnesses [e.g. the kid who got slapped] of a piece of the ground itself, in the literal sense of a hand-to-hand passing of an amount of soil, a twig, key to a building on that land, or other token.”
— David Grace