In the second episode of Foundation, in a scene where Hari and Gaal are talking in the meeting/conference room in between court sessions, Hari asks Gaal if the "hook" hurts to which she replies that "I try not to wiggle".
I'm confused as to what this 'hook' refers to. I initially thought it's some sort of restraint used by the Empire, but the only restraint we see them use is the "shroud" which is itself only used when moving people around and Hari and Gaal are clearly not shrouded during those conversations. It may be a reference to the books, but I don't really remember it (and I read the books ages ago).
I find this hook thing very confusing. It's mentioned twice and we are not given any context as to what it means, so why even include it?