A filler is any word or sound that interpolates (i.e., is inserted into) the main message of a speaker. Common fillers include "um", "ah", "like", "so", and "you know?", among others. Excessive use of fillers in scientific presentations can reduce the credibility of the speaker as well as impair the comprehension of the speaker's message by the audience. Primary causes of fillers include nervousness/speaking too quickly, inadequate preparation time, and infrequently used words that are difficult for the speaker to remember while presenting. Recommendations for reducing the use of fillers include self-awareness of the problem, reinforcing feedback, and active intervention to render pauses silent (instead of verbal) by "chunking" content, increasing preparation time, and slowing presentation pace. Excessive use of fillers is an obstacle to becoming an effective public speaker and therefore, efforts to reduce filler use should be a goal of professional development.