‘Can I have a helicopter that’s got spots like a leopard?’

‘Yeah, if you just sit still and don’t scratch your head, all right?’

Ben nodded. ‘All right.’

‘In a second I’m gonna go so small you won’t see me,’ I said. ‘But I wish you won’t be scared, OK?’

‘I won’t be scared.’

‘No, you won’t. Right, so I wish I was really small, about twice as big as a nit, and I wish I was in Ben’s hair, and I wish I had a sharp, shining sword of just the right size!’

The next instant I was in a brown forest, with big strands of hair as thick as my arm sprouting up all around me, droplets of water as big as coconuts clinging to them and a forest floor of pink scalp.

I heard Ben’s voice, loud and echoey in the tiled bathroom, commentating on the situation quite calmly. ‘Sam’s gone. He’s gone small. He’s in my hair. He’s killing nits.’

I made my way through the forest, following the pink paths through the giant hairs, looking all around, sword at the ready. I heard a kind of scritching noise and steered towards it. A moment later I came face to face with my first nit. Or head louse, to use the correct terminology. The nits are the egg cases, I know that really. But everyone just says nits for the whole lot, don’t they?

Well, I’d thought ants were ugly. But compared to nits, the ants were film stars. Beauty queens. Visions of loveliness.

The nit, or louse, in front of me, was around the size of a large dog. It had two wiggling antennae, six waving legs that ended in claws, and a fat tail like a fish. It looked like it was made out of some sort of semi-transparent jelly. You could see all the blood swirling around inside it. Its face – well, I don’t know whether to call it a face, exactly – was soft and doughy, with a black oval eye on each side. Like something out of a nightmare. Its mouth parts were plugged into Sam’s scalp and it was sucking greedily. You couldn’t imagine a more repulsive creature. No one could like it. Even their own mothers don’t like them. They just lay their eggs and crawl off to a different part of the head.

I walked right up to it. The stupid, dumb creature just carried on sucking.

‘This is the end of the line for you, nit!’ I said.

But I don’t think it heard because they don’t have any ears. I plunged my shining sword into its side. A pale liquid gushed out, streaked with blood. The creature wriggled, but carried on sucking. I cut its head off, and it finally stopped.