[Rebel_Ace]

“When you point the finger at someone, you have four fingers pointing back at yourself.”

Not to be too nit-picky, but you only have three.
Unless you contort your hand, when you "point", the thumb aligns with the index finger, leaving just three fingers pointing back.

[MUDDOG]

When the thumb points upward, it’s the normal to the surface spanned by the boundary curve oriented in the direction of the curved fingers.

[PhiloBedo]

My thought,too. I think the “four” helps some understand he’s talking about their own hand.