About this, the dev had a q/a where he was asked what the meaning of Sen was. He responded that there was a hint in the mental ward + what dum says.
In the mental ward behind there counter in the first area, there is a hint/advice/floor sign that says redrum, the common reversable of murder. Tweedledum says the player doesn't have enough "dum" when you first talk to the twins in their room. In japanese she says damu, which combines a bit better with sen than dum.
Yeah that's why I pointed it out.
Yes, in the scene where he tells you to run from red hood. If your sen is below the understanding threshold, instead of his gibberish translating to run away it instead translates to "The Crawling Little Girl". I haven't checked but I bet his boss dialogue also translates to something else, especially if you have edith's ring equipped.