Bolero: An example of ostinato

The 2nd graders have been talking about (and practicing their own) ostinatos (repeated musical patterns). Today, I showed them clips of the biggest ostinato example I know: Bolero by Maurice Ravel. Listen to the snare drum rhythm at the beginning. Then the flute comes in with a melody on top of it. The melody moves over to the clarinet, and the flute starts playing the same rhythm as the snare drum. This kind of trading around grows more intricate as the piece goes on, but the ostinato in the background never goes away. 

Check out this video and see if you can pick out the ever-present ostinato: