If Pacquiao's head doesn't snap back when punched by JMM...
I saw the last fight again.
Everytime JMM lands a punch at Pac, Pac's head snaps back.
When Pac lands a punch at JMM, JMM's head is steady.
That's why audience/spectators thought JMM won the fight.
If JMM's head snaps back everytime Pac lands a punch, you could have seen it a lot of times than Pac's head snapping back.