In this paper, we explore how exertion interfaces can promote physical creativity and the role that this might play in performative interaction. In particular, we are interested in exploring how to design and develop devices and applications which use physical interaction, or exertion, to promote performative interaction or the witting transitions between observing, participating and performing. Using the Nintendo Wii as an exertion interface, we are updating, analysing and representing a small selection of clapping games found in the Opie Collection of Children TMs Games and Songs in the British Library and emerging from ethnographic studies of playgrounds in London and Sheffield, UK. We describe the Physics of clapping and associated technical issues, the design of a low-fi, open source exertion interface and the analysis of a participant study. We suggest guidelines for designing for physical creativity, namely kinesthetic literacy, performative interaction and believability, and conclude with a discussion of future considerations.