Some of these cables can contain thousands of wires and pulled tight as a drum at times, making using your fingers to get at a specific set of wires a real challenge. I've found that using one hand or closed needle nose pliers as a wedge to separate the bundle, I can slip the hook in with the knife parallel to the bundle and then twist it 90 degrees behind my wires to grab the ones I need. Then it pulls my wires to the front with ease. For this picture I picked a relatively small cable to keep one hand free for my phone camera, but generally when I resort to doing this it's a big cable that's a pain to deal with. (btw... this is also useful on wiring harnesses on vehicles as well)