Everybody is on a diet

I recently purchased a Roomba, a vacuum cleaning robot that goes around the apartment and swallows all the dust it can find. There is a light called 'dust detector' that lights up when it detects some particularly crunchy and deliciously dirty spot. I have seen the same mechanism in people's eyes, it's called a 'sugar detector' in that case.

Alas, Roomba often stops in the middle of its meal with another light blinking: 'Dieting'.