A goal of the survey interview is to collect reliable and valid data. Achieving this goal is often difficult because respondents may not understand what is being asked of them. In traditional interviewer-administered survey modes, interviewers can pick up on signs of confusion and difficulty answering a question from the respondent’s speech patterns, expressions, or response times. In self-administered surveys, however, identifying confused respondents has previously not been possible. The introduction of Web surveys provides an interactive environment with a vast amount of data that researchers can collect in real time. Using these data, it may be possible to determine when respondents are having difficulty answering a question, much like in an interviewer-administered survey. Using Web browsing and education research as a basis, this paper identifies 11 unique movements that respondents make with the mouse cursor while answering survey questions. Through an exploratory analysis, we hypothesized which of these movements are related to difficulty answering survey questions. Then, using scenarios to manipulate question difficulty and asking participants to rate the difficulty of each question, we were able to test our hypotheses to determine which movements are related to difficulty and which are general movements people make when interacting with a computer. Finally, this paper proposes a model that can be used to predict, in real time, when a respondent is having difficulty answering a survey question. We find that not only are certain mouse movements highly predictive of difficulty, but they are more predictive than response times, which have been used to predict difficulty in the past. This information can be used to provide real-time help to confused participants or it can act as a diagnostic tool to identify confusing questions.