This is how Jack counts: 1 - 2 - 3 - 4 - 6 - 7 - 8 - 9 - 10.
He gets points for consistency and an unflappable confidence that we are wrong. Don't even try to reason with him--pointing out that he has five fingers, five toes, and that there are many other everyday items that require the number five, will only result in a complete meltdown of emotion.
Frankly, we are beginning to believe him. It is easier than arguing with a three-year-old who knows everything.
P.S. He also claims he can speak spanish.