When a piece of tracing paper is placed gently on the surface of a bath of water,
it rapidly curls up from one edge and rolls up due to the swelling of the side in contact with
water. With time, as the swelling front propagates through the thickness of the paper, the paper
gradually uncurls itself and eventually straightens out. We analyze the experimental dynamics of
rolling and unrolling of the paper and complement these with a minimal theory that explains the
basic observations. Our study might be useful in the context of designing biomimetic devices that
work as actuators or harness energy from humidity variations.