Courtney Humphries writes it better than I can retell it:

Thom Verhave, a psychologist working at a pharmaceutical company in the 1950s, tried to apply pigeons to an onerous aspect of commercial production: quality-control inspection. Touring the area where capsules were manufactured, he watched as about seventy women examined each capsule one by one on conveyor belts, discarding the “skags,” capsules that were dented, misshapen, or discoloured. Figuring that pigeons could do the same task, Verhave proposed the idea to the director of research, who had just managed an expensive but failed attempt to use a machine to inspect capsules. Verhave was given permission to develop a demonstration device, and he trained two pigeons to recognize common defects and report if they spotted one. Within one week of training, both birds were inspecting capsules with 99 percent accuracy. Their performance garnered visits from higher-ups at the company, but soon the board of directors quashed the project. Even if it worked, who would buy drugs from a company that used pigeons for quality control?

(From Superdove, pages 91-92)