This is one of the videos shown to great tits as part of the study, which influenced how the birds that saw it selected their food.
The video shows an adult male trained to eat artificial prey of a paper package containing a piece of almond.
The square on the package marks this out as 'conspicuous prey'. The piece of almond within the package has been soaked with a bitter-tasting fluid, to mimic the foul taste of conspicuous prey in the wild.
The bird shakes its head and beak-wipes. This is the reaction of 'disgust' from which the other birds learned to avoid square packages in the test aviaries.