In today's modern world, bugs in software systems incur significant costs. One promising approach to improve software quality is automated software verification. In this approach, an automated tool tries to prove the software correct once and for all. Although significant progress has been made in this direction, there are still many cases where automated tools fail. We focus specifically on one aspect of software verification that has been notoriously hard to automate: inferring loop invariants that are strong enough to enable verification. In this paper, we propose a solution to this problem through gamification and crowdsourcing. In particular, we present a puzzle game where players find loop invariants without being aware of it, and without requiring any expertise on software verification. We show through an experiment with Mechanical Turk users that players enjoy the game, and are able to solve verification tasks that automated state-of-the-art tools cannot.