Could a parent’s decision to vaccinate a child depend on a free bag of lentils? The premise seems implausible:immunization can be a matter of life and death, and a bag of lentils is worth only a dollar. Yet a randomized controlled trial in India showed that a gift to parents of a 1 kg bag of lentils and a set of plates can dramatically raise the percentage of children protected against major disease (Banerjee et al. 2010). Providing a quality immunization camp alone increased the percentage of fully immunized children from 6% to 18%. The addition of the lentil and plate ‘incentives’ raised the figure to a whopping 39%. How can we explain the outsize effect of a gift of everyday household items?