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.
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