Don't see it? The flaw is revealed below...
The boy has six fingers!
When I was a kid I would often draw hands with too many (or too few) fingers, or I'd put the thumb on the wrong side. I thought I had outgrown this type of mistake – apparently, I was wrong.
This sketch became the cover of an educational book about Independence Day. Thank goodness the extra digit was caught early – that's not the sort of mistake you want to discover after a book has been published!
Final (5-fingered) art below. Thanks to Teri Weidner for her ability to count fingers correctly!