Introducing cosmic-ray science to the general public is a challenging task. In particular, the operating principles of Imaging Atmospheric Cherenkov Telescopes (IACTs) may result confusing and puzzling to students who wonder why these huge optical instruments cannot take beautiful images of astronomical sources. To overcome this issue and learn about IACT astronomy, we propose an innovative solution which is particularly modern and engaging: "Flashes", an educational game on a web application developed ad-hoc by the cultural association PhysicalPub. "Flashes" is based on the physics behind the Cherenkov technique. Atmospheric flashes recorded by IACTs have different shapes depending on their source: hadron, gamma, muon or "else" (car flashes, sky background, electronic noise, and others). In our game, the player is presented with Cherenkov images from real scientific data and simulations, and must classify them according to their origin, trying to mimic the real image discrimination analysis. The game is divided into several sessions, each dedicated to one IACT among the main ones currently in operation: ASTRI-Horn, MAGIC, and LST-1 (Large-Sized Telescope prototype for the CTAO). In every session, the player has one minute to recognize the highest number of images and get the highest score. Several topics related to science education are involved, such as critical thinking, artificial intelligence, and uncertainty of science. "Flashes" supports multiple-player sessions and includes an introduction that educators may use for preparatory explanations. "Flashes" is accessible using a URL from any internet-connected personal device. It is completely free and does not require any account.