Live chickens? Do not blow at their anuses.

Avian flu: how to avoid. For your consideration:

• When buying or handling live chickens, try not to touch them or their droppings. Do not blow at their anuses.
• Egg shells may have been contaminated with bird faeces. Wash the outside of eggs and wipe them dry before putting into the refrigerator for storage.
• Observe food hygiene when cooking live chickens and eggs.
• Always wash your hands thoroughly with liquid soap and water after handling live chickens and eggs.

Those bullet points are from one section of the very excellent Hong Kong Government Centre for Health Protection Avian Flu FAQ. But it is that first bullet point that has got me puzzled. Any chicken experts out there? I am sure there must be a good reason. Does it chill out an anxious chicken? Why would anyone want to 'blow at their anuses'? Please tell. Thank you.