This isn't the first time I have heard cut your fingernails. Apparently some people will actually look just to see if you took the time to pay attention to details such as this.
Personally, I would recommend being personable. This seems intuitive, but I am suggesting that you recognize and act knowing that both the interviewer and interviewee are people. Don't give robot answers that you read online and everybody else also uses. Be yourself and let your passion for pharmacy come through.
If you were invited for an interview, your credentials (GPA, PCAT, ECs) are adequate. The interview is more of an opportunity to see if you really care and to see the person behind all the numbers they have already seen. Be relaxed and show that you are a person and not just a list of credentials.