The use of tritone and minor 7th motifs all over West Side Story. Once you start noticing them, they are everywhere. Tritones signaling tension, incompatibility, hatred, and strife with the 7ths contrasting with hope, peace, and a chance to escape the fate. And just how discordant they feel when in medleys really emphasizes the struggle, and the option to how to resolve the finale can literally change how the entire show feels.