Early last year (!) I made a prototype of an adjustable giraffe model. A telescopic giraffe in box 

I've been mulling over the mechanism but never really got anywhere. Anyway, yesterday Hugo's forum post reminded me about the giraffe. That and my new mushroom model intersected nicely.

Pneumatics! That could be that answer. So, a quick sketch and section of telescopic tubing later and I think I have the start of a new model.

Should be a fun one!