The texture of vellum is really fascinating. It's very different from paper, you can feel it's almost alive (well, it's animal skin anyway). You can see it nicely on this zoom.

Here the scribe crossed out the word "Babilonis". I'm not sure if it was a way to correct an error (like he forgot to write the word "filia"), or if it was done to enhance or put some focus on the word, a sort of old underlining. I would say the second possibility, because I have another example on the german 15th century brevarium.