Could they hear them scream? Depends on the gas chamber in question. In Majdanek, the gas chamber had a viewing port for the operators. In Auschwitz, it was an

Could they hear them scream? Depends on the gas chamber in question. In Majdanek, the gas chamber had a viewing port for the operators. In Auschwitz, it was an underground bunker. Did they have to clean up the corpses? Nope, that's what the Sonderkommando were for. Jewish prisoners who cleaned up the corpses and operated the crematoriums. Why they used Zyklon B - god only knows, but they didn't use just Zyklon B. They also used carbon monoxide and car exhaust gas quite frequently (mainly on the eastern front and early on in the war)