I've heard allegations that the boring pile of "salad" that often accompanies burger and chips in, er, less reputable places, and which is invariably left uneaten on the edge of the plate, is routinely fluffed up with a fork in the kitchen and shovelled on to the next punter's plate.

As for the greasy containers of ketchup and mustard on the table, I regard those in most cases as dangerous and untouchable objects.