Before you hear a single line of dialogue, you hear it: that three-note whistle, ominous and predatory, the last thing you want to hear on a dark New York street in the middle of the night. It belongs to the Jets: a way of signaling to each other that there are buddies nearby and warning everyone else to steer clear.

That's not the only signal; there's the finger snaps too, which we see in the very first shot of the Jets and continues through the whole film. It's very beatnik – dig those crazy sounds Daddy-O! – but it also serves the same purpose as the whistles: we're Jets, we're brothers and when we move, we move as one.

Take a look at "Cool," the big number where the Jets try to keep it together after Riff buys the farm. The finger snapping puts some order back into the chaos. Individual Jets break with the program and cease their finger-snapping ways, only to be brought slowly back into line by Ice (who's calling the shots with Riff gone). A-Rab, Action and others want to "bust" – run out screaming and cut themselves some Shark steaks. But Ice slowly brings them back into line.

The song starts out with just Ice snapping his fingers, and slowly, one by one, they all start snapping their fingers too. When individuals get out of sync, he slowly brings them back in, until they all head out into the street, once more snapping in time. It conveys the idea quickly and in a very, um, cool fashion without having to spend time explaining it all with dialogue. At the end, we understand exactly what's happened: it's Ice's gang now, and they're back in step.

No dissention in these street punks' ranks.