I recently watched this classic musical, my all-time favorite movie, for the 10th or 20th time. You know the scene where the children are hanging from trees as Captain Von Trapp and the Baroness drive by? Listen closely. Just before the kids disappear from view, you can hear a "woo-woo-woo-woo." The "wild" children are acting like "savage" Indians.
The scene above is as the car is approaching. I'm talking about a few seconds later, when the car is leaving the children behind.
At that moment, the kids are too small to see them clearly on-screen. The most prominent one could be Friedrich, the oldest boy. The whoops seem to come from his vicinity. One of his hands is free and hovering near his mouth, so he could've been doing the war-whoop gesture.
Or it could be Louisa, the second oldest daughter, since she's about the same size. The figure has something on his or her head, which could be the scarf Louisa wore. With its loose end, it looks a bit like an Indian headdress.
The hand gesture and the headdress may be illusory, but the sound is clear. At least one Von Trapp is whooping like an Indian.
Whoops in the Alps?
Someone questioned this, saying:
War whoops are the universal sign of savagery! That's how we know the children were out of control!