“I came to test the automatic soap dispenser, but it only dispenses soap after I take my hand away,” Giulia said. She was a retiree who wrote detailed reviews of ordinary things because she had free time and glasses for reading small instructions. This time, her subject was the new dispenser in the local library restroom.

Giulia held her palm under the nozzle. Nothing. She moved it closer to the sensor—still nothing. When she withdrew her hand, the dispenser thoughtfully dropped a portion of soap straight into the sink. Giulia tried again, faster this time: palm under nozzle, pause, palm away. The soap landed on her sleeve.

To catch the third portion, Giulia held her other hand to the side and quickly pulled the first one back. The dispenser remained silent. She leaned down to see whether the sensor was lit, and that was when the soap landed on her glasses. Giulia straightened up, found the tap by touch, and began rinsing the lenses. The tap sensor also demanded movement, so the water ran only while she waved her free hand in front of it. This was inconvenient for washing, but looked very convincing as a farewell.

The librarian brought paper towels and inspected the dispenser. Its sensor had been installed backward. She turned it around, and the soap finally landed in Giulia’s palm on the first try. Giulia gave it two stars: one for cleanliness and one for teaching her to remain alert in a restroom. The problem was solved, and the sleeve was washed that evening.