Zyklon-B

Zyklon B (German pronunciation: [tsykloːn ˈbeː]; also spelled Cyclon B or Cyclone B) was the trade name of a cyanide-based pesticide infamous for its use by Nazi Germany to kill human beings in gas chambers of extermination camps during the Holocaust. The "B" designation indicates one of two types of Zyklon. The other was "Zyklon A" – a liquid pesticide which released hydrogen cyanide in a chemical reaction with water.

In the parodies
The chemical was referenced in at least a few parodies, and is the "gas" referred to when Hitler has to pay the gas bill for snuffing out undesirables. Both Himmler and Fegelein was also known to have used the said chemical in their antics, such as when they laced most of the bunker crew's marijuana with the pesticide.