my experience with my old gelding was essentially an experiment to see whether i could teach him to play soccer with a yoga ball! since i sold him before i could finish, he still hasn't quite mastered 'kicking' it, but we made quite some progress in our time!
month 1:
month 10:
and here's another
video of his nose-touch in action as he was being introduced to the larger ball! i definitely had a good time teaching this 'silly' trick to this horse and learned a lot about positive-reinforcement training in horses so that i might apply it to more useful skills. from this behavior i shaped 'targeting' which was useful for things like clipping and bridling; if he didn't want something near his face i could ask him to target it to get his brain in the right place. i look forward to starting up clicker work with my younger horse and hopefully i can eventually try it under saddle! i actually have started with this horse on targeting behavior with the end of a dressage whip:
as for clickers, the truth is that the generic "clicker" is just a tool of convenience. the truth is, anything can be a clicker if you make it so; a bell, a snap of the fingers, a tongue-click, even just the word "yes" or "good boy/girl." you just have to make sure the reinforcement is constant! so if you're going to make "yes" your marker/click, make sure every single time you say "yes" you give a reward, and be careful that you don't accidentally say "yes" if you don't mean it, even if you aren't talking directly to your animal!
but yeah, for all anyone cares you could use "noodles" as a marker word, so if traditional clickers aren't your fancy, experiment with different noises until you find something you and your animal both like!