In Generation V, there is a chance of a critical capture, where the Poké Ball will only shake on the ground once, thus providing a higher catch ratio. When a critical capture occurs, the Poké Ball will pause in mid-air, shudder, and make a metal noise. Critical captures occur about as often as Critical hits, making them quite rare; however, even with such a small chance of occurring, a critical capture still presents a massive boost to the overall chance of capture for Pokémon with a catch rate of 3, who may have odds as low as .4%.
However, a critical capture is not a guaranteed catch. It is possible for critical captures to fail, especially with Pokémon of lower catch