If you only watch one CataractCoach video this month, this is the one I encourage you to study very carefully. The first time I experienced the snap sign I was a junior resident and I was operating with a professor who was equally lost. Right after attempted hydro-dissection, there was a sudden snap in the anterior chamber where it shallowed and then deepened in the matter of a second. A few moments later, the nucleus was in the vitreous cavity. What happened? The posterior capsule suddenly ruptured during hydro-dissection and that causes the snap sign. This anonymous video shows this very clearly and we replay it in slow motion. You must be able to instantly recognize the snap sign and then know how to recover. Even better is to prevent the snap sign. Risk factors for the snap sign include a small capsulorhexis, a defect in the posterior capsule (posterior polar cataract or damage from a prior intra-vitreal injection), and blocking the ability for the nucleus to prolapse by placing your blunt cannula across it.