Swinging your legs or shifting in the chair. Wandering eyes, especially when you are being addressed or giving a direct answer. Slouching, closing your eyes or looking downward in a manner that would convey disinterest. There is no consistency from one interviewer to the next. Styles and approaches vary.
Most interviews are open and non-combative.
Honesty is key. Be prepared for questions on any variances in your application. Don't list any honors, research projects, or volunteer experiences in your application that you will be unable to support in your interview as real and significant. Ask questions if you have real ones about the school. Read the school catalogue prior to the interview.