10 years ago I wrote a book for O’Reilly that remains one of my favorites to this day. The book—Your Brain: The Missing Manual—is still in print, and every once in a while I get an email from a reader who’s stumbled across it and discovered something weird and wonderful about the squishy gray matter inside our heads.

When it comes to human weirdness, I love pretty much every topic. But if I had to choose just one favorite part of Your Brain: The Missing Manual, I know what I’d pick.

At the ti...