I remember him telling me once of something that, he said, had just happened to him at the railway station. He was early for a train, so he bought The Guardian, a cup of coffee and a packet of biscuits, and sat down at a table, putting the folded newspaper down so he could do the crossword. The packet of biscuits was in the middle of the table.
There was another man already sitting at the table and this man now leant calmly across, tore open the packet of biscuits and ate one. Douglas said he went into a sort of state of shock, but determined not to show any reaction he equally calmly leant forward and took the second biscuit. A few minutes later, the man took the third and ate it. Douglas then took the fourth and tried his best not to glare at the man.
The man then stood up and wandered off as if nothing had happened, at which point Douglas's train was announced. So he hurriedly finished his coffee and picked up his belongings, only to find his packet of biscuits under the newspaper.
It's actually a profoundly philosophical story. With one slight adjustment of the furniture, the victim becomes the aggressor and the aggressor the victim, and one is left with the untold story of the true victim hanging in the air. It's exactly the sort of shift in perspective that fascinated Douglas as a way of not just telling stories but also of looking at ideas.
He told me the same story many times, and it eventually ended up, much embellished, in So Long and Thanks for All the Fish.