Setting is modern-day Japan, specifically Shibuya, with some some crazy supernatural stuff going on behind the scenes that most normal humans are unaware of.
I've Googled: "choking bruises", "choking injuries", "choking to unconsciousness", various similar phrases and all of the above with -judo at the end; "how to gag someone" and a few other gag-related things, but I ended up with mostly sexual results. Most of what I found and read was about child abuse, judo, and teenagers strangling themselves to get high...
I've also looked through most of the medicine tags here, even not-entirely-relevant ones (learning random things is fun!).
The character getting injured is male and appears to be a pretty scrawny fifteen. He's been captured by an eighteen-year-old male who's significantly stronger physically. The eighteen-year-old wants to utterly humiliate the fifteen-year-old and make him miserable by whatever means possible, but he wants his prisoner fully conscious most of the time (because he'd be boring otherwise) and, if possible, able to walk. The story requires the prisoner to be able to stand around, talk a lot, and pick up a gun and shoot someone a maximum of four days after the abuse ends.
I have ideas for general injuries that would fit (though more ideas are always nice!), but there are two things in particular I'm not sure about.
One, my notes keep using phrases like "the ring of bruises around his throat" or "the bruises that circled his throat", as at one point the prisoner was held against a wall by his throat with enough pressure to knock him out; I'm having a hard time finding out what someone's throat would look like a few days after they've been choked, and I'm not sure this is accurate. I realize now that it wouldn't be a complete ring, but would there be a solid line of bruises across the front of his throat, or...?
Two, I'm having trouble thinking up ways to shut the prisoner up that don't involve knocking him unconscious. He's wonderfully sarcastic and not the type to keep his mouth shut, and I'm thinking it will get on his captor's nerves after a while. I've found some useful stuff on gags, but I was wondering if there were any injuries that wouldn't be terribly dangerous but that would make it difficult to speak for a short period of time. I don't really know how to search for this.
And a much less serious question that I really don't know how to search for...
I need some mathematical words or phrases that could be used as insults or profanity. I'm hopelessly math-stupid, and I could just go with what little the canon gives, but that would be boring!