How to do tooth whistle in beatbox?

The tooth whistle is a mouth position that creates a high pitch screeching noise.

How it's done:

1) Do the 'f" sound and prolong it

2) While you're making the 'ffffff' sound, create a small hole between your top teeth and your bottom lip

3) Shift around the position of your bottom lip until you get a small squeak or whistle noise

4) Since this is only a mouth position, you can layer with it humming and throat bass