1) Flaps 1) Horse focuser 2) Horse racing accessories 3) Perception obscurers 
[poultry] Blinders, also known as peepers, are devices fitted to, or through, the beaks of poultry to block their forward vision and assist in the control of feather pecking, cannibalism and sometimes egg-eating. A patent for the devices was filed as early as 1935. They are used primarily for game birds, pheasant and quail, but also for tur...
Audience blinders - high intensity flood lights mounted to focus on the audience. Turned on to create an impact on the audience and perhaps cover a scene change. 
Blinders are a special diffusing light you arrange in your staging area to mask the stage during scene changes.