And this is one technique that I like the most, and I see from a source that discusses all sorts of ukulele, this technique is just like on a guitar, only to perform this technique on the guitar should be accompanied with a walker or guitar accessories form, tremol.
And on the ukulele itself, this technique is done only with the help of hand / right arm you with a way to touch a part of the body ukulele, ukulele and after touching the body give it up and down pressure, and the result sounds like a wah-wah effect or tremol on guitar, and video below will explain in detail on the technical arm-wah for the ukulele, happy listening.