Alexis. "The crowbar arrived at CERN, Freeman received it, world saved." Reddit Blog. 20 Nov. 2008 http://blog.reddit.com/2008/11/crowbar-arrived-at-cern-freeman-was.html
"Anti-Mass Spectrometer." Combine OverWiki. 22 Nov. 2009 http://half-life.wikia.com/wiki/Anti-Mass_Spectrometer
"Armadillo Run." Armadillo Run. 19 Aug. 2009 http://www.armadillorun.com/
"Black Mesa Incident." Combine OverWiki. 13 Nov. 2009 http://half-life.wikia.com/wiki/Black_Mesa_Incident
"Combine." Combine OverWiki. 25 Nov. 2009 http://half-life.wikia.com/wiki/Combine
"Gordon Freeman." Combine OverWiki. 23 Nov. 2009 http://half-life.wikia.com/wiki/Gordon_Freeman
P., Andrew. "GameSpot's All-Time Greatest Game Hero Draws to a Close. And the Winner Is..." Gamespot. 15 Oct. 2009 http://www.gamespot.com/greatest-video-game-hero/index.html
Palmer, Grant. Physics for Game Programmers. New York: Springer-Verlag, 2005.
Purho, Petri. "Crayon Physics." Crayon Physics. 2008 http://www.crayonphysics.com/
"Source Engine Features." Valve Developer Community. 28 Feb. 2008
"Xen Crystal." Combine OverWiki. 20 Nov. 2009 http://half-life.wikia.com/wiki/Xen_crystal http://developer.valvesoftware.com/wiki/Source_Engine_Features#Physics
Headcrab on front page: http://www.spore.com/view/myspore/FireGriffin