This is a twist on the popular lab where students build a hand with cardboard, straws, rubber bands, etc. In this lab I give students no directions for how the hand should be built. Groups decide on their own criteria for a successful hand after brainstorming about essential hand functions, then design and build a prototype that satisfies their criteria. Students are asked to think of data to collect and then revise their design several times to get the most effective possible prototype. This is just the student worksheet, no teacher directions as it is fairly self explanatory.