You resent this machine, and I understand, but consider what it is asking your body to do: coordinate a barcode with a laser at exactly the speed of light. The red beam sweeping your cereal box is a coherent stream of photons, each one born inside a semiconductor when an electron dropped between energy levels and paid out the difference in a single packet of light.
That drop is quantized. It cannot happen halfway. Every "beep" is a few trillion electrons agreeing, discretely, to fall.
The scale that weighs your bagged apples is measuring the gravitational tug between the Earth's entire six-septillion-kilogram mass and one piece of fruit, and it is accurate to a few grams. You are running a planetary-scale gravitational experiment to confirm you did not steal an onion.
And the touchscreen. When your fingertip taps "card," it does not actually touch anything. The outer electrons of your skin and the outer electrons of the glass repel each other before contact, so what you feel as a solid press is electromagnetism holding you a fraction of a nanometer above a surface you will never technically reach. The screen senses this by watching your body distort a grid of stored electric charge, because you, being mostly saltwater, conduct.
The machine keeps insisting there is an "unexpected item in the bagging area." There is. It is you: a warm, briefly assembled arrangement of hydrogen forged minutes after the universe began and heavier atoms fused inside dying stars, standing in fluorescent light, mildly annoyed, holding a coupon. The item was always unexpected. Fourteen billion years of physics did not have to produce a thing that could stand here and be irritated at a robot.
It did anyway.