Situational interest has been identified as an important motivational variable that has an impact on students' academic performances, yet little is known about how the specific variable of the learning environment might trigger students' situational interest. The purpose of this study was to investigate sources that stimulate the interest of students in an undergraduate course in zoophysiology. Observations, informal conversational interviews, and responses to a survey were used to identify sources of interest. Five situational variables and one predominantly individual variable are documented to influence the catching of interest of students. The situational variables are live animals, "Ah-ha!" experiences, meaningfulness, social involvement, and humor, whereas the predominantly individual variable is background knowledge. We conclude that the situational variables are largely under the control of the faculty and should be considered when planning instruction. By focusing on the enhancement of situational interest in physiology lessons, faculty members can find ways to foster students' involvement in specific content areas and increase levels of academic motivation.