Chicken sunglasses

Invented in 1939 to control cannibalism:

These small glasses with red lenses were designed to be held on the chicken's beak with a cotter pin through the nostrils of the bird. As a cannibalistic animal, chickens are provoked by the sight of blood and will peck at each other, eventually killing off much of the flock. These red lenses prevented chickens from seeing the red blood and calmed their behavior. These have not been manufactured for many years and we do not have any available for sale. These glasses are now considered a collector's item.

Found here