The / unasked questions / eventually are answered

    "The common active ingredients in a hot chilli are chemicals belonging to the capsaicin family. When these chemicals make contact with the capsaicin receptors on the cells in your mouth, you feel the burn. Birds, on the other hand, have absolutely none of their receptors on their cells, so they feel no pain from eating chillies. This means that birds can cheerfully eat chillies and then spread the seeds around the countryside. Chilli seeds that have passed through the gut of a bird germinate better than chilli seeds that are planted by hand. In fact, while there's something about the mammal gut that stops chilli seeds from germinating, the opposite is true of a bird's gut. Birds usually excrete while they are feeding on another bush, so the chilli seeds often land on shady soil, their preferred environment."

Dr Karl Kruszelnicki: The Good Weekend, 12/2/06.