Talking science is based on the premise of being serious and dignified. Still, both teachers and students use humour when they communicate. However, little is known about the mechanisms of how learning science is constituted when teachers and students are using spontaneous humour in science classroom activities. In this study, we acknowledge this gap. We have analysed video data using practical epistemology analysis (PEA) from two different contexts in physics education, a physics classroom in grade 9 and a group of undergraduate students learning basic mechanics together. The findings showed that spontaneous humour, such as absurdities, supported the learning process in two ways: (1) orienting talk and action towards the scientific purposes of the assignments and (2) sorting out what scientific content and norms were/were not of relevance in the situation. The results illustrate how the participants made jokes to clarify how reasoning and actions tallied with the task at hand. These humorous situations positively affected students' ability to act intentionally towards the aim of the activity, and the results show that this way of joking can have positive consequences for student learning. Therefore, humour ought to be viewed as a significant resource for learning in the science classroom. Doing science can, like any other activity, be a humorous endeavour in itself, without cartoons or extravagant shows.