A.D. Amorosi With Lionsgate’s “The Hunger Games: The Ballad of Songbirds and Snakes” looking to continue its reign at the top spot of the box office, it’s time to consider the most sonorous secret to its success: its original, bluegrass-tinted song selection, including a theme written and produced by Dave Cobb (with lyrics from “Hunger Games” author Suzanne Collins), and sung soulfully by the film’s star, Rachel Zegler.