I usually introduce this one just by telling students that we are going to make a craft project. We spend about 5 minutes snipping at soda straws, and then I show them how you can make them squeal by blowing into them, and the students have a blast. At the end, we discuss how oboes and saxophones work in the same way as their soda straws. What they made was essentially a soda-straw oboe.
To make a soda-straw oboe, you simply cut a pair of reeds into one end: flatten one end and crease the sides as best you can, then snip away the corners, making two pointy triangular flaps, like this:
The exact size and shape of the flaps isn’t critical, but they should be reasonably symmetric and not too short. Also, I have found different performance with different brands of soda straw. The plastic in some is a little firmer and harder to crease, and those straws don’t work quite as well.
To play the oboe, you place the reeds inside your mouth and pretend you are biting down on the base of a duck’s bill. With your teeth or your lips, press the bases of the two flaps close together, and then blow as hard as you can. Depending on the flexibility of the plastic, and on how you shape your mouth, you may be able to produce a variety of squawks and squeals.
In my experience, the novelty of noise-makers wears off pretty soon unless you can actually play different notes. How can we make our straw oboes play different notes? I have tried fitting a second, ever-so-slightly larger straw over the first, and making a “slide-oboe”, but the two straws have to be very close-fitting or it doesn’t work. I (and my students) have also tried snipping holes into the sides of the straw. We can’t play recognizable melodies, be we can at least make different notes come out by uncovering one or the other of the holes. (It is only the closest opening to the mouthpiece that matters, so it doesn’t do much good to leave them all uncovered and cover them up one at a time.)