The purpose of this study is to explore a theoretical idea in relation to a body of empirical material from a reading activity involving a picturebook on shadow. The theoretical idea, sprung from variation theory, entails children's discernment through synchronic simultaneity as a key to their ability to imagine. To explore this idea, an analysis has been conducted on how 5-year-olds, in words and actions, express themselves in a reading activity involving "The Black Rabbit" (Leathers, 2014) in regard to discerning and imagining about shadow as a light phenomenon. Vygotsky describes children's previous experiences as a key to their ability to imagine. The results of this study imply that children's discernment in the moment, with synchronic simultaneity, appears to be another key that unlocks their ability to imagine explicit depictions in a picturebook. The results also show that when children's discernment with both synchronic and diachronic simultaneity (i.e., discernment in the moment and before the moment) is missing, their ability to imagine remains untapped, as none of the keys to their imagination, which might unlock their ability to imagine implicit depictions in a picturebook, are used.