"What is?" Susan says, looking over my shoulder, which is something I've hated since primary school, when Miss Jamieson, as suited to teaching as I am to international diplomacy, read sneeringly aloud my fleeting ambition to be a flower-arranger.
Jamieson had a booming voice and a chest like Ben Venue and as a seven-year-old I was equally scared of both. I never got the hang of keeping her happy. Quite the reverse. She'd be driven at times to heights of maniacal frenzy I have not encountered in my life as a grown-up.
"Kids, women, engineering," I tell Susan.
"Ha!" she says and wanders out to the garden, which is looking lovely at this time of year. Pink roses, yellow honeysuckle, purple clementine ... I suppress my inner flower-arranger and get back to the story.
So your brain has three main parts: the cerebrum, the cerebellum and the brainstem.
The cerebrum is the grey, wrinkly bit you see in all the brain pictures. It has two hemispheres - the northern, where most people live, and the southern which has penguins. No, hang on.
The cerebrum has a left hemisphere and a right hemisphere. These are connected by a bundle of nerves called the corpus callosum. If a surgeon cuts this, which used to be a treatment for epilepsy, the halves can behave like two people in the same body. One guy even got stuck in a loop, with his left hand pulling his trousers down and his right pulling them up again.
And here's a strange thing. The left hemisphere of your brain controls the right half of your body and the right controls the left. Nobody knows why. Maybe God read the wiring diagram wrong.
But I have a better theory.
Flatfish such as plaice and flounder have two eyes on one side of their body. They don't lie on their tummies on the seabed, as you might think, but on their sides. So as a flatfish develops, one eye migrates round to the other side of its body.
I believe something similar happens to our heads. They start off facing backwards, with brain and body halves aligned. Then nature looks down, sees heels instead of toes and realises it's cocked up again.
So it slowly turns the whole head around. The face is now in the right place but the brain is back to front, relative to the body.
Now you might think this is a stupid theory. I'm pretty sure you do. But plenty of seemingly stupid science theories turn out to be true. Time travel, quantum mechanics and evolution, for a start.
And I have evidence to support my theory. When I worked at British Aerospace my section head Dennis Anderson told me a story about the manager director, whose mum he knew well. When this guy was born they got a big fright, she'd told Dennis, because he seemed to have no face.
"It was a terrible shock," Dennis said. "Then the midwife took a closer look and found it. What a relief! His whole face was round the side of his head. Over the next week it gradually migrated to the front and he's been normal ever since. In fact, he's a high-flyer, as you know."
Now babies' skull bones are malleable and a tough birth can squeeze them out of shape for a while. My own head was squished pretty flat when I was born. There was some talk of sending me home by post, to save money, and getting me popped through the letter-box. But my mum didn't have a stamp so we had to go on the bus.
A face right round the side of the head is different though, and I think it's strong evidence for my theory.
"What theory is that?" Susan says, coming in from the garden with a bunch of pink roses and reading over my shoulder again.
"The human face starts out at the back of the head," I tell her.
"Yours should have stayed there," she says, heading through to the kitchen to find a flower-vase and laughing like a drain.