Sometimes recurring themes pop up in an author's work and the author is the last to spot them.

I was in a school recently, telling the students about my new book Girl Underground. I described how the two main characters, Bridget and Menzies, go out into the Australian desert and dig a tunnel into a refugee detention centre to try and rescue their penfriends. Then I told the group about my next book, Worm Story, which I'm finishing off at the moment. It's about an intestinal worm looking for love. To save his community, Wilton goes on an intrepid journey down a human intestine and eventually emerges into a huge bright outside world he didn't even know existed.

As I was saying all this, I started to notice a strange expression on the faces of some in the group. The sort of expression people get when they've just spotted something and they're not sure if you have. I did a quick check to make sure I hadn't left off any crucial articles of clothing.

No, everything was there. So what had the group spotted that I hadn't? I didn't have a clue until a student put up her hand.

'Do you put tunnels in all your books?' she asked.

I stared at her, mind racing. She was right, Girl Underground and Worm Story both feature tunnels. Was the same true of my other books? Have I been a tunnel nut without realising it?

The group quickly came up with more evidence.

• Keith and Tracy try to tunnel out of a collapsed opal mine in Worry Warts.
• Limpy, Goliath and Charm travel along a spooky drainage tunnel in Toad Heaven.
• In Gift Of The Gab, Ro gets trapped under an unexploded shell in a deep trench that's almost a tunnel.
• There's at least one tunneling incident in Wicked and at least two in Deadly.
• Ginger doesn't dig a tunnel in Teacher's Pet, but several students were pretty sure she thinks about it.

I had to admit that tunnels do appear in my books fairly regularly. Naturally the group was curious about why this was so. Had I ever worked in the mining industry? Did I spend any part of my childhood trapped in a tunnel? Did I secretly wish I was an intestinal worm?

I was able to answer no to all their suggestions. But I wasn't able to answer their question, why tunnels? All I could say was that for me the creative process has many mysteries and they'd just shown me another one. Then I went home and tried to think of an idea for a new book with absolutely no tunnels in it.

Until next time, oo-roo and happy reading (and tunneling),

23 September 2004