The left thumb points to where the asparagus spear is likely to break. But the cut mark shows where the asparagus starts being tender. We learned about this from watching Laura Calder’s TV show “French Cooking at Home”: Use a very sharp knife and starting near the bottom of the stalk, hit straight down from above to find where the asparagus is no longer tough.
We used to bend asparagus and allow it to break at its natural point, theorizing that this is where the tender part starts. But because of the way the asparagus is pretrimmed at the vegetable store, there’s a LOT of waste that way. […] To trim the asparagus, rather than breaking it in half, use a sharp knife to cut away the tough part of the asparagus. Starting at the blunt end of the asparagus spear, gently tap against the spear with the sharp part of the blade until the knife wants to cut through. I hope that made sense!! (We are forever indebted to Laura Calder because now we get to eat more of the asparagus that we buy.)
-me, trimming asparagus, blog from OUR kitchen | Steamed Asparagus with Butter and Lemon, June 2010