Well I can try to remind you if I know at the right time that it's needed!
I mainly enjoyed Tom's experiences himself, wasn't really so interested in the female ponies but of course that's just personal preference.
I was particularly taken by all the invasive inserts - can't stop thinking about the spikes in his sinuses - the removal of his voice and then on top of that the silencing shock collar. And the blackout contacts and the ever tightening arm restraint. Where to go with those? I'd love the looming threat (that should eventually be fulfilled after a long build up!) of totally removing his arms and even his eyes if he does well without them - which he seems to.
Coping with all those things at once, whilst performing pony duties and training too, must be such an intense experience, I'm surprised he doesn't break down more, but I guess to begin with he's just completely overwhelmed. He'll probably start trying his safeword action again, and if it was me, then I'd gratuitously misunderstand it as fidgeting, and then fit him with a movement sensor, so that whenever he isn't supposed to be walking somewhere, eating or otherwise working, he has to stand to attention (or lie still) and any unauthorized movement whatsoever would be punished with multiple shocks (which themselves must be endured without sound or movement - except of course where they directly cause muscle spasms). Perhaps during longer periods of waiting he'd get a five minute break to go and drink water etc but the start and end times of this would be somehow challenging to identify... Finally I'd use similar movement sensors to ensure that when he's walking (not running though) he lifts his knees up high with every single step. The ability of automatic sensors to monitor and enforce behaviour mercilessly and with iron consistency is surprisingly hot!
The things going on in the lower half of his body are vital to the story too, but they seem mainly more standard affairs, and I haven't got any specific ideas for them. I mean, I guess you didn't even ask for any of my ideas at all, but this is where my thoughts go when you ask me about my favourite parts so far!
And of course he needs a team partner, whose arrival he would see but he'd be totally incapable of warning him, and once he was also fully set up as a pony, this would be followed by long periods of motionlessly and silently looking at each other without any way of actually enjoying each others' company in their lonely existence...
