I saw West Side Story as a kid in 1961. It was out-of-this-world powerful. Later at home, I listened to the LP soundtrack a LOT. The Prologue was/is especially captivating. Above goes to a 9:51 minute film version of the Prologue (with the very end clipped). Below is a visual representation of the 6:32 minute original August 1960 soundtrack recording. The transition beginning at 4:32 turns up the heat. The zylophone phrase begins at 4:34. See how many different zylophones you can detect that begin riffing off each other starting at 4:44 and running through 5:07.