At first, chaos as a whole was responsible for the split time, but they decided on uncertainty as a cause solely to serve a joke about flathead/Phillips head screwdrivers.[8] "When you're talking about how to define chaos, let alone uncertainty, that's [when] you get into a semantic spiral," producer Ryan Ridley said.[9] Harmon felt it a suitable source for the time split because uncertainty was "an intersection between quantum physics and [the] human condition."[10] The team was happy when they created the joke that Rick believes his parallel self is plotting to kill him, because it "felt like [we] were writing a cartoon."[11]