Bb Wobbleaka
Texas Skake
This is quite simple, basically you finger an Eb but without the LH 3 G key:

You then need to blow quite hard with an exaggerated vibrato so that the note alternates between G and Bb with a yodelling effect. It should sound a bit like this:
| Tenor |
| Alto |
For some interesting saxophone multiphonics, try playing this fingering without the octave key.