Rapid-fire missiles is a technique in Metroid Prime whereby Samus can fire missiles much more quickly than usual. There are two ways to do it. The fastest and easiest way to do it is to hold up on the C-stick; doing so will allow Samus to shoot missiles very fast, although she will still be limited by the limit of three missiles in the air at one time. Another way to do it is to press A after firing each missile, which cancels the missile launch animation and allows Samus to fire another missile. This method is inferior because it is both slower and harder to execute.
Parasite Queen can be killed extremely fast using this method.