this is safa's brain, that's marwa's brain.we need to achieve is effectively untwist the brains, and that is difficult, pretty difficult to do just in your head. but it is perilous. the bbc was given unique access to chart the complex medical and ethical choices made... this is the day, the moment of truth, and everything hasjust got to be perfect. ..in the hope of giving the girls independent lives. safa and marwa are 21 months old, and were born in pakistan. they have come to london's great ormond street hospital with their mother zainab, grandfather and uncle, and are under the care of neurosurgeon owasejeelani. it is clearly very difficult to go through life when you are joined together like that, so it does make a very persuasive case in favour of doing the surgery. the family are very clear on that. clearly, life being separate is very much better than life together. if we felt there was not a very, very high chance that we could do it safely, we would be thinking about whether we should do it or not. i think the whole te