Illegal immigrants admittedly come in many guises. But even as a novel disguise, it cannot be often that a teenage migrant from China would drink only water but not consume any food, fail to respond to any question, behave in an agitated manner, and urinate in public. That, indeed, was how 15-year-old Hong Kong resident Yu Man-hon behaved while being interrogated by an immigration officer. Just why the officer failed to see such unusual behaviour as signs of mental impairment was alarming. Or maybe he did suspect Man-hon was mentally retarded. But since there was no record of his departure, he was first 'found' by the Shenzhen side, and as a perfunctory check with the local police turned up no suitable match, it was decided to shove him back to the other side. Whatever efforts officials made on the Hong Kong side of the border, they jumped to an entirely wrong conclusion. As a result, a mentally handicapped boy has spent several days wandering about a strange city, apparently begging. First detained by the Shenzhen police, then released but unable to reach his home, the confusion and discomfort the boy must be suffering can only be imagined. Without seeking to be too harsh on immigration officers, already under criticism for blunders involving 'illegal immigrants' who turned out to be nothing of the kind, this is the latest example of the hazards of working on the assumption that any unusual case should be treated as suspect. Surely, Shenzhen police should also share some blame for handling the boy callously. Having picked him up, they also did not bother to check his identity. No doubt people who are trying to cross illegally will resort to any subterfuge to conceal the facts. But one of the skills of well-trained staff should be to tell the fraudulent from the genuine. In this instance, they have undoubtedly failed. Given the boy's mental impairment, it might not have been easy to establish the facts of the matter. But if there were communication difficulties, that was all the more reason to take the time needed for independent checks. Once again, caution and compassion seem to have been lacking at immigration counters. But all that matters now is to find the boy and bring him home. The single thought in his parents' mind will be that their son is returned safely, little the worse for his ordeal.