"That's a special modifier that we forgot to hide for this demo," explained Valve's Chet Faliszek, with marketing VP Doug Lombardi then describing it rather vaguely:

"Take Portal for example: We had our best internal players who could blow through that game in about 30 minutes, but within weeks of launching it we had people on YouTube beating [the testers'] times by 10 minutes or more. Realism is for those players."

The zombie shooter sequel hits PC and Xbox 360 on November 17, backed by a $25M ad campaign and enough hype to guarantee you'll hear plenty more about it before then.