Working memory is critical for learning but has a limited capacity for processing new information in real time. Cognitive load theory is an evidence-based approach to education that seeks to minimize the extraneous (unnecessary) load on working memory to avoid overloading it. The "seductive details effect" postulates that extraneous load can come from instructional design materials that attract interest but are unrelated to, and impair, learning. Presentation packages, such as Microsoft PowerPoint, have built-in decorative animated "GIFs" that are designed to make presentations more visually appealing. The aim of the study was to investigate the effect of such "decorative" animations on learning and working memory performance. We found that students were less able to recall content presented in the presence of a decorative but relevant animation compared with a still image. This effect was found with two different topics (human physiology and enzyme kinetics). Compared with still images, students also found it harder to remember animations themselves, and the self-reported mental workload required to remember them was higher. These results show that decorative animations are seductive details and are thus a source of extraneous cognitive load.