- Why Do Clocks Run Clockwise?: And Other Imponderables
- Do Penguins Have Knees?: An Imponderables' Book
- Why Do Dogs Have Wet Noses? An Imponderables Book
- Life's Imponderables: The Answers to Civilization's Most Perplexing Questions : Why Do Clocks Run Clockwise? When Do Fish Sleep? Why Do Dogs Have Wet Noses?
- A World of Imponderables: The Answers to Life's Most Mystifying Questions