Louis CK and Jon Stewart go back a couple of decades in comedy together, so last night’s appearance on The Daily Show allowed the two comedians to reminisce a bit. They also — spoiler alert — discuss the fart joke that’s a central plot point in the premiere episode of season two of FX’s Louie.

Let Louis CK break it down for you why farts are funny. Safe for work? Even merely explaining farts makes Stewart laugh uncontrollably, at least when CK does it; also, when he describes in detail just how obesely obese he plans to get once his career in comedy is over.

“You don’t have to be smart to laugh at farts, but you have to be stupid not to.” — Louis CK

Roll the clip!