Worlds smallest Ukulele? (Prototype) 97,6mm / 3,84"

It all startet when we went to the music store, I needed some stiffer Reeds for my Saxophone and my wife spontaneusly bought a Ukulele. (the first string instrument in our household, she usually practices E-Piano)
At home, we both had fun with that tiny Instrument and she asked me if I could build a small model Ukulele to put on her keyring. I'm not an instrument builder, but I have practice in building small things, eg. for the puppet's house of my niece.
So I startet with my fretsaw, some sand paper and a piece of 5mm thick aviatic plywood (birch, 2 layers per mm thickness) and cut the outline of a Uke. Body, Neck and headstock is made of one single piece of wood.
As I sanded the body blanks, some kind of demon must have ridden me and give me the idea try make a functional Uke in this size. So I sawed the Uke's body hollow and glued a bottom and top wood (0,3mm veneer, cherrywood) on the body. Added saddle and some frets to the neck/fretboard and started the first prototype with just 2 Strings, which are made of stretched spring wire (which easily breaks when it's bent to a small radius)
This is the result: my first prototype of the worlds smallest Uke.
I sawed a few more blanks, the next one will be made with maximum resonance chamber, more detailled and maybe I try with 4 strings.
(Btw: if anyone has a useful idea how to make some simple tuning mechanics in this scale, please leave a comment.)
At this moment, the strings are pre-tensioned with some small pliers, then hold in place by a small bamboo-peg, stickin together with the string wire in a dia. 0,5mm hole on the headstock, and it's all secured with a drop of instant-glue. No chance to adjust the pitch, not even roughly...
Please sorry for the acoustic recoils, I had to set the microphone very, very sensitive to capture that small acustic signal... (that sensitive microphone setting also the reason why You can hear my breath so loud. I'm not asthmatic...)