The alchemical puzzler Opus Magnum has a few of us at House RPS scratching our heads and shouting "a-ha!" before giddily sharing our twisted contraptions in GIF form. It's real good, friends. The studio behind it, Zachtronics, is headed by Zach Barth. I spoke to him about the game's machines, his short stint at Valve, and the reasons he sold his own company.