I personally don't know of any studies that deal with the impact of swallowing a piece of string. If you have retained an attorney, he or she will usually do research and find an expert, likely a gastro doctor, to address the issue of whether or not swallowing a piece of thread is or can be harmful. From what I know about these types of personal injury cases: you have to show that damage (financial physical and/or psychological) has occurred as a result of swallowing the string, and you have to prove a certain degree of neglicence on the company's part. But the main issue is one of damages. Did you suffer any? Did you have to go to the hospital, underwent tests, missed work as a result of swallowing this piece of thread, etc.?
Rose