Two valves to the half-life
Two shots through the portal
Quite complex wordplay, as Valve is a well-decorated, American video game and software development corporation. Half-Life and Portal are popular games produced by Valve, and both happen to (currently) have two main installments (Portal, Portal 2, Half-Life, Half-Life 2). Additionally, both games involve shooting (“two shots”).
As well as being a popular video game series, it could be worth mentioning that half-life is also a scientific term to describe the time it takes for something to decay to half of its original state. Thirdly, it could be thought of as literally half of a life.
The lines are fuzzy in terms of actual meaning. Although a stretch, to go along with the sexual innuendos and theme within the verse, two valves (behind the aforementioned “backdoor”) could refer to a vagina and anus, with “two shots” then referring to ejaculation. Or he could simply be playing video games.
Also the human heart has four valves, so if two are missing you are half dead, which is like two shots outta four to get thru the portal to the afterlife
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