This article attempts to address the challenge that preschool teachers face, when integrating a specific content area, science, with play. The study builds on the theoretical framework of Play-Responsive Early Childhood Education and Care (PRECEC), in which teaching, and play are understood as a mutual activity. In this mutual activity, teachers and children signal their participation by shifting between "as if" (fantasy and fictional worlds) and "as is" (acquiring knowledge of the world as it is) (Pramling et al., 2019). The empirical data consists of video-observations of a preschool teacher and 1-4-year-old children who participate in activities that incorporate play and scientific content. The video-observations were analysed through studying how and why shifts between as is and as if were made by the preschool teacher. The results show that the preschool teacher made the play shift between "as if" and "as is" through different types of actions (voice change and bodily expression). Further, shifts seemed to be made with two aims in sight: science learning and socialisation. In conclusion, the preschool teacher (as a more knowledgeable adult) has an important role in creating a responsive environment and in introducing science content, which does not arise by itself. Implications for preschool teachers and preschool practice are discussed.