Scientific literacy involves not only reading and writing, but also knowledge of other discipline specific ’semiotic resources’, such as, diagrams, graphs, equations, etc. In this paper we base our discussion of scientific literacy on Airey and Linder’s (2009) ideas about fluency in critical constellations of disciplinary-specific semiotic resources. This is illustrated by a discussion between three physics students. In their discussion, the students tried to explain why a stick partially immersed in water appears to bend at the water surface. Despite drawing a diagram commonly used in problem solving in this area, the students could not formulate a satisfactory explanation. Eventually, the students agreed on using a different diagram. This quickly led the students to a satisfactory explanation. We conclude from our analysis that despite apparently being fluent in the required semiotic resources, the students had not yet reached the level of scientific literacy where they spontaneously knew which resources were needed.