What does Hari Seldon mean by 'the hook'?

Question

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?

Answer 1

Earlier in the same scene Gaal refers to herself as a piece of bait set out by Hari to provoke the Empire into finally acting against him, e.g. now that someone who finally understands his math has arrived on the scene and can be consulted and/or used against him.

The hook in this instance isn't literal. She's just referring to the trap that Hari has set (the court case, followed by the exile of Hari's followers to Terminus) with herself as the thing that will provoke the Empire into falling for it.

Gaal: Did Hari bring me here as bait? Because I can prove him wrong?

Lors: He’s not wrong, Ms. Dornick. But yes on the bait part.

Obviously as a water-worlder, her first thought when it comes to baited traps is fishing. Had she been from a forest world, she might have referred to herself as being hung from a tree.