I meant tool. I much prefer using a dedicated eraser over the little smudgy excuse they usually mount on the end of a pencil. Now that I've already invested in a gross of refills for my standard Pentel click eraser, I've discovered what I like even better.
When I make Celtic drawings, I do a lot of erasing. Not because I am inaccurate, fickle, or sketchy, but due to the nature of construction. I don't weave those paths around in my head ahead of time. I lay everything out then establish what is over and what goes beneath. Consequently, I have many lines and crossings to adjust, and I've learned not to tempt fate and make them as I'm inking.
I found this gem in a Japanese market in Portland. It's a Tombow mono knock 3.8 and it's absolutely perfect for getting in those tiny spots without destroying all the lines in a two inch radius. I'm in love.