The matter was so unusual that it restored a degree of innocence to an audience very practised in the genre of the adversity documentary, an audience which broadly thought it had seen everything. Well, it hadn't seen this... and besides, the film was powerfully structured by the countdown to the day on which the two girls were separated.
That event governed all thoughts and it made the film unusually pure in its concentration. Everything was taken up by thoughts of the future - the immediate future of the two girls after the operation and the speculative future they might have as adults if they weren't separated. The tussle between those two imponderables ensured that most of those who watched were not just engrossed but somehow implicated in the decision. The follow- up film, in which Galloway returned to see how the only survivor of that operation was coping, satisfied a lasting sympathy with the family but it couldn't hope to offer the same degree of fascination. Memory, regret and hindsight had muddied that initial clarity.
Both Mary and Liam Holton said they were convinced that they had done the right thing. But any other conclusion would surely be unthinkable for a parent, grieving anyway for the loss of a much-loved child. As it happened, Katie turned out to have a weak heart, which allows both parents the strange consolation of another alternative future, one in which they would have lost both girls if they hadn't gone ahead. Even so, their sensible refusal to pick over the decision appeared understandably shaken by a meeting with the Hensels in America, a family who have conjoined twins and have decided not to opt for surgery.
The remarkable sight of two children in one body, brought back vivid memories of the ordinary charm of Katie and Eilish - the slightly guilty start you felt in the first film at the realisation that they liked feeding ducks and blowing through straws like any other child. Eilish looked on at this projection of her own recent past with an entirely unfathomable stare. Was it simple grief for her own sister (who died, after all, when Katie was three - on the very cusp of a child's permanent memory)? Or was it something more complex - a vision of completeness rather than strange excess?
QED's film, The Fall and Rise of Sergeant 'Reggie' Perrin (BBC1), was far more conventional in its form, another contribution to the rehabilitation documentary. It was, though, a pretty gripping one, following the attempt of a disabled ex-Marine to climb Mount McKinley. Alan Perrin is almost blind and paralysed down the left side as the result of an accident with a faulty hand grenade. "A year ago," he said, "my greatest ambition was to be able to walk to the toilet." Now, with the help of some friends, he was trudging his way to the summit of America's highest mountain, a peak which had already claimed six lives that year. He didn't make it to the top, sensibly stopping before he risked his own life, or that of others, but the achievement was startling even so. The most remarkable thing was the suggestion that determination might be a therapeutic drug - it appeared that what was left of his brain had begun to rewire to move his left leg, as if the cells had been nagged into obedience by that unremitting will.