Teaching about the nature of science is seen as a priority within science education, and has also been highlighted as a suitable context for challenging the most able ("gifted") learners at secondary school level. This article discusses a practical session designed to introduce the idea of physical (natural) laws. The session asks students to explore patterns in three physical systems--capacitor discharge, cooling, and equilibration of pressure in two joined columns of water. These activities were chosen because they could all be conceptualized in terms of feedback cycles and exponential decay, and so had potential to show how similar patterns are found in diverse physical phenomena. The session was taught as part of an after-school enrichment programme for 14-15 year-old students who were nominated as "gifted" by their city comprehensive schools. The session is reviewed in the light of student responses, which suggested that it made suitable demands for the most able students. The session also has potential, with suitable modifications in teaching approach, to contribute to teaching about the nature of science to students of a range of abilities and ages. (Contains 2 tables and 2 figures.)