Given the task definition and input, reply with output. In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: A couple of years ago on a hot summer day in south Florida, a little boy decided to go for a swim in the old swimming hole behind his house. In a hurry to dive into the cool water, he ran out of the back door, leaving behind shoes, socks, and shirt as he went. He flew into the water, not realizing that as he swam toward the middle of the lake, an alligator was swimming toward the shoe. His mother in the house was looking out of the window and saw the two as they got closer and closer together. In great fear, she ran toward the water, shouting to her son as loudly as she could. Hearing her voice, the little boy became worried and made a return to swim to his mother. It was too late. Just as he reached her, the alligator reached him. From the bank. the mother caught her little boy by the arms just as the alligator _ his legs. That began a tug-of-war between the two. The alligator was much stronger than the mother, but the mother was much too determined to let go. A farmer happened to drive by, heard her screams, raced from his truck, took aim and shot the alligator. After weeks and weeks in hospital, the little boy survived. His legs were extremely scarred by the attack of the animal and on his arms were deep scratches where his mother's fingernails dug into his flesh in her effort to hang on to the son she loved. The newspaper reporter, who interviewed the boy after the injury, asked if he would show him his scars. The boy lifted his pants legs. And then, with obvious pride, he said to the reporter. "But look at my arms. I have great scars on my arms, too. I have them because my mom wouldn't let go.
Answer: an alligator
The boy's legs were scarred by _ .