The interviewer wants to hear about how you heard of the company, and they want to see that you took the time to research their organization. Tell the interviewer what caught your attention when visiting the company website. Maybe you have a friend that works for the company; explain what that friend told you that made you want to work there. If you have heard great things about the culture of the organization or are interested in a specific research program or possible growth opportunities with the company, this would be a great time to bring it up. You'll want to demonstrate that you took the time to look into the company before interviewing by giving specific examples of things that piqued your interest while doing research.