Halfway through the meal, von Igelfeld spilled a small amount of gravy on the cuff of his shirt. Attempts to remove the stain with his table napkin having failed, he asked permission to use the tap in the bathroom for this purpose. ‘I know exactly where it is,’ he said. ‘Please continue for a few minutes without me.’

He went out into the long, book-lined corridor that led to the bathroom at the back of the house. Halfway down this corridor, sitting strategically on the carpet, was the Unterholzers’ dachshund, the unfortunate Walter, with his three-wheeled prosthetic appliance strapped round his sausage-like stomach. On seeing von Igelfeld approach, Walter rose to his remaining foot and attempted to wheel himself out of the way. He was not fast enough, and von Igelfeld, who was not looking where he was placing his feet, tripped over him.

The dog gave a yelp and attempted to move further out of the way. Unfortunately this was not possible, as von Igelfeld’s foot had kicked off one of the dog’s wheels. Now unbalanced, the dachshund simply fell on his chest, letting out a whimper as he did so.

Von Igelfeld looked down at the dog at his feet, its little wheel clearly detached, lying beside him. Bending down, von Igelfeld picked up the wheel and, calming the dog as best he could, attempted to fit it back on the appliance. It was very stiff, and he had to give it a good push before it found its place, but this had the effect of driving all the breath out of the dog, who had to gasp for air.

The wheel in place, von Igelfeld gave the dog a further push, to see whether all was working correctly. It was not. The wheel that he had replaced now refused to go round at all, so that the dog turned in little circles as he paddled with his remaining leg.

Von Igelfeld had no difficulty in arriving at a diagnosis: the wheel needed oiling. But how to do that?

The dog, in the interim, had moved in circles through the kitchen door, and it was in the kitchen that the solution presented itself. Reaching up to the shelf above the sink, von Igelfeld took down a bottle of extra virgin olive oil and dripped a small quantity over the bearings of the non-functioning wheel. Then he tried to ease the wheel by spinning it. Unfortunately he forgot that he was holding an open bottle of olive oil in his other hand, and as he leaned forward he tipped the contents of this bottle all over Walter and the surrounding parts of the kitchen floor.

Walter, alarmed by being covered with olive oil, let out a howl of protest and ran – in so far as a dog with a prosthetic appliance and three wheels can run – back along the corridor and into the dining room, to seek the succour of his owners.

Von Igelfeld put the now empty bottle of olive oil back on the shelf, made an unsuccessful attempt to mop up the spillage on the floor, and returned to the dining room. The conversation was still in full swing, although Frau Unterholzer was looking down in puzzlement at the floor beside her chair where Walter, covered in olive oil, was licking at his coat. She glanced up at von Igelfeld and frowned, but he avoided her gaze.

At the end of the meal, Professor Unterholzer left the table to turn on the coffee-making machine in the kitchen. A moment or two after his departure, there was a loud thud from the kitchen. Frau Unterholzer gasped and hurried from the room, to return a few moments later with her husband, who looked flustered and uncomfortable. They both glared at von Igelfeld.

‘My husband slipped,’ said Frau Unterholzer. ‘But he is uninjured.’

‘I’m so sorry to hear that,’ said Herr Huber. ‘At my aunt’s nursing home they have these special non-slip floors. You can’t slip on them – it’s just impossible.’

‘If one covered them with olive oil, one might,’ said Frau Unterholzer darkly.

‘Possibly,’ said Herr Huber. ‘But why would one do a thing like that?’

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