A presentation explaining inner workings of the source engine, and how they are exploited by speedrunners use to try to finish the video game Half-Life 2 in the fastest time possible. The source engines other-worldly physics provides a fascinating and mathematically defined world that speedrunners have come to understand and manipulate in ways that were never intended by the creators of the game. Exploiting (and understanding) this engine has led to "runners" learning skills that are unique to source engine games, and extremely fun!