When you&rsquo;re a kid, there are lots of things you&rsquo;re not supposed to do. But what if you didn&rsquo;t really do any of those things, what if you just imagined them? Then it wouldn&rsquo;t matter if your supposings were silly, impossible, or even a little naughty&mdash;because they&rsquo;re all just in your head. Alastair Reid&rsquo;s book is a monument to the liberating power of unfettered thought. Here he reunites with a frequent collaborator, the famed illustrator and designer Bob Gill, to muse on the possibilities:<br><br>Supposing I read a book about how to change into animals and said a spell and changed myself into a cat and when I climbed on the book to change myself back I found I couldn&rsquo;t read. . .<br><br>Supposing I had a twin brother but we never told anyone and only went to school half the time each. . .<br><br>Supposing a very beautiful lady fell in love with me and wanted me to marry her but I just yawned and said Maybe . . .