Here is how you can find out if you’ve given the wrong amount of money to a disheveled septuagenarian convenience store clerk in Japan.
First, she spreads the coins out on the little mat so that they’re all visible. Once this is done, she counts them very slowly six times.
That should tip you off. They usually only count the money three or four times. If she counts more times than that and the counting slows down slightly each time, this means something is wrong.
Around the final coin counting, the mood and energy of the convenience store shifts. There is a disturbance in the wa. She stares fixedly at the coins with furrowed brow, as if trying to translate the characters of an ancient dead language written on a tortoise shell.
At this point you may hear a low muttering or chanting. It is coming from her. Once the sound increases in volume to become barely audible, you realize what she is saying. She is saying the price on the cash register display alternating with the wrong amount that you have given her. She has led you to the realization that the change is wrong without breaking the peaceful feeling and actually telling you.
You realize now that you were 100 yen short.
Digging the 100-yen coin out of your wallet, the tension in the store disappears. Everything in the universe is okay again.