Is The Video Of Two Brothers Pranking Their Little Sister About A Zombie Apocalypse Fake?

Millions have viewed the video of two brothers attempting to convince their sister that a zombie apocalypse is underway after she has her wisdom teeth removed but is it fake?

Like most everyone else, I laughed hysterically at the two brother's trolling their little sister but notice one brother's lips move along with his sister's at 1:43 and again 3:03.