Butterfly Guard Pass

While in your opponent's butterfly guard:

Underhook one of their legs with the same side arm, and hug the hip with the other arm. Lift your leg on the side with the underhook, bringing it back down with the other side's foot trapped against your hip. By the way of your choosing, collapse the leg on the side with the trapped hip, passing to side control. Quickly work your way up before your opponent can work an underhook or reverse triangle.

Fairly simple, yet new to me.