Want to know how Guinness ensures its canned beer has a draft-style head? Why inhaling helium makes people sound like chipmunks? How samurai were able to unleash the perfect sword hit?

John Swain’s your man.

The associate physics professor does regular spots on Canada’s Discovery Channel on a show called The Daily Planet. In a segment known as “Fact of the Matter,” Swain explains the physics behind mundane things like how to swing a golf club or get tarnish off silverware, why a boomerang comes back, and why it’s tough to wade through water.

For the past several years, Swain has made quarterly trips to Toronto to tape his segments. Occasionally, the spots appear in this country on the Discovery Science cable channel—sometimes he’s even recognized on the street here.

Swain’s favorite bit? Explaining how the small ball with a hole put inside every can of Guinness gives the beer a thick, creamy head. “We cut one open,” he says. “The thing sprays a jet of gas.”

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