I used to think any coax with a decent signal reading at the tap would be fine. Then I found a line from 1982 in a condo that passed signal but had so much noise the modem kept dropping. I mean, the jacket crumbled when I touched it. Now I just assume anything older than me is gonna be a problem.

Read a fishing blog that mentioned those little knives are called hankotsu blades. Japanese fish markets use them a lot for precise work. The brand Tojiro came up a few times for being sharp and not crazy expensive. Might be worth checking out if you want something like what you saw.