Ever wonder what is being advertised by a new giant poster featuring a tanned and super-fit Aaron Kwok Fu-shing, near the Causeway Bay entrance to the Cross-Harbour Tunnel? I was confused until erudite reader John Ma - who turns out to be a doctor - wrote to enlighten me on this intriguing advert. BCS, from Japan, stands for Bowel Cleansing System. 'I wonder how many readers know the nature of the product advertised by the new billboard, showing a prominent Aaron Kwok and a female model, with their arms raised akimbo above their heads,' he wrote. 'You may think they are advertising an antiperspirant, but you'd be wrong.' So that's the secret of Aaron's abs? At least BCS is to be orally ingested - it sure beats a colonic irrigation.