Why Should Notes Even Bend?

Stupid question. I haven’ thought about this for a long time… but why should a reed of a fixed length even be able to produce 2-3 different notes? After all, in the end, we’re just inhaling… drawing the air through the hole in one direction.

I do recall once looking at a stripped down harp in a mirror as I played and noticed that the two reeds in a single hole were vibrating. Maybe I dreamt that part. It might have been 30 years ago.

Is there some sort of interplay between the reeds that creates the different notes?

What are the physics involved?

You can find explanations all over the internet teaching the physics of bending.
Bending (there are more bending techniques than just draw bends on hole 1 - 5)
is usually the product of the interaction on the draw and blow reeds caused by
your changing airstream and oral cavity shape. If you want to play much on the
lower forty of a diatonic (suck harp), you will have to bend. There is bending on
other holes, both draw and blow, to get different notes and effects.
If you want to play all the range of the instrument without bending, try chromatic
harmonicas. With the slide out, it plays complete major scales from bottom to top.
With the slide in, you get all the accidentals. I can get accidentals on any instrument,
but that’s another use of the word.