It is exactly what he does. The crabs have no chance to even get near her, no matter how insistent they are on it. Fëanor is quick and efficient. The pile of carcasses around them is growing with each stupid creature trying, and failing, to get past him. All the time it took him to get here resulted in one thing above all else. He had perfect crab demise to an art form.

"Concentrate on opening those cages, we will handle things down here."