|The following is based on Fallout Tactics cut content and has not been confirmed by canon sources.|
It is a special perk, meaning that it is not available upon leveling-up. It was designed to be acquired by playing a minigame that was planned for the Pip-Boy. When a "twitch" appears above the player's head, it is supposed to give the player a free action, at an AP cost of zero.
You are a master of Pip-Boy games. You have unsurpassed reaction speed with your thumbs!