Caprice Kir is a finnish liquor. It is a blackcurrants apertif and it is pretty common in nordic countries. The liquor consists of 13% alcohol and that is why the limit for "Game of Life" is a 13% alcohol. It has been previously documented that participants in the game have downed a whole Kir bottle when called out. The "kir-limit" is needed because it could be complicated if a participant takes a sip out of a vodka bottle, for example, without marking it beforehand. According to the rules the whole vodka bottle should in that case be downed, but the "kir-limit" saves you from that.

If someone breaks the rules of "Game of Life" by drinking from an unmarked drink, you can call them out by simply saying "Game of Life". There is not much more to it, you can call out multiple people at once but they have to be called out separetly, i.e. you have to say the phrase "Game of Life" each time you call someone out. 

A mark can be just about anything. A common mark is to twist or pull of the can tab from a can of beer. A mark is essentially everything that alternates the drinks original look. If you drink from a bottle you can mark it by ripping of a bit of the label, if you drink from a glass you can put a straw in it (if it did not come with a straw originally). You can be very creative with the mark, just about everything is allowed!