So far the posts are very interesting from an evolutionary and behaivioral point of view. Agamids generally are purely visual hunters, that is, they eat prey based only on its form and movement, with underdeveloped olfaction and taste. However chemical discrimination ability has been re-evolved in those species which became omnivorous, probably to be able to distinguish between good and toxic plants, and as a consequence it was useful for animal prey too. Acording to a study I read, bearded dragons have re-evolved some chemical discrimination ability.
However that ability is much less developed than in other lizards, mainly active hunters. In a study I read about the toxicity of fireflies to dragons, it was stated that bearded dragons aren't detered by any insect regardless of its taste except for the burning ones. And I have read also that they will avoid burning plants like raddishes. So they can distinguish chemically between foods, but still the primary sense is vision.
If you payed attention to the intended pood items, most are high contrasting small areas on a unicolor background like nails or scars, small moving objects like fish and small animals and sheet or leaf like objects or projections of objects, like papers, bags, ears of stuffed animals etc. All these are biologically relevant, as they resemble the foods consumed normally in the wild. High contrast objects seem like flowers and fruits, moving objects seem like insects and small animals, and sheets or flaps resemble leaves. I cannot make a hypothesis about hair, but perhapse they eat mosses or lichens in the wild when food is scarse. Probably there is some morbidity or even mortality due to wrong food ingestion in the wild, but a relevant study there has not been conducted. So we must be careful of our dragons.
ps. Chilli peppers do not affect reptiles and birds. Capsaicin, the substance that activates the pain receptor and gives the false sensation of burning, has evolved to affect only the mammalian receptor, as mammals are more likely to chew and destroy the seeds of the plant, but birds will mainly swallow the fruit and defecate the seeds intact elsewhere.