Ingredients:
1 bendy straw
1 bath or shower
1 child
Directions:
1. Place child in bath or shower. Wet down child with water, paying attention to the sides of child’s torso.
2. Bend bendy straw.
3a. Place short end of bendy straw in child’s mouth.
3b. Place long end of bendy straw between child’s arm and torso in the area commonly known as “the armpit.”
4. Instruct child to blow.

And the end result is???????????????
(I think I know and I also know E does not need to have any more ways to make this sound–he does it naturally, just fine, thank you.)
You should put that in the HUHO wiki.
Bonus points if you wet down your own armpit and join in the fun.
You know, we’ve got video of your excellent instruction that we could put on YouTube — at no cost to you. Let us know.