Scientific knowledge is tentative and open to revision. This sense of tentativeness, or changeability, is missing in the way textbooks and teachers often portray the nature of science (NOS). Instead, students are left with the impression that the scientific method produces sure knowledge and that they can uncritically accept the knowledge because it was created--or discovered--via the scientific method. However, it is equally important for teachers to accurately and consciously portray NOS in almost everything they do when working with students. To illustrate this point, this article looks specifically at how laboratories can help students better understand NOS and describes two lab activities namely, chromatography and mystery powders, that can have a huge impact on the students' view of science.