This little clip is known as the Book of Mormon HAKA. HAKA is a dance that the Pacific Islanders would do just before a battle. These missionaries adapted the dance to using the Book of Mormon. The words are:
Take the Book from your Back
Slap the Book on your Chest
Read the Book, Read the Book
We've got the Gospel
No matter what they say
You walk in the water with me.
I understand that there is a recording somewhere with President Peterson doing the HAKA with our Elders - I'll try to locate!
On Youtube you can find some great recordings of the HAKA at Sports Events - pretty intense.