Warning - graphic description: I have seen what cats look like after being killed by gassing, it is a gruesome sight. Cats and kittens are loaded into wire cages, which are then placed inside the gas box. The lid is shut and the gas is turned on. Kittens, climb to the top of the inside of the wire cage and are found dead with their paws sticking up through the top of the cage, their jaws tightly clamped down on the wire. I have seen litters of kittens in with the mother cats. They died with their eyes wide open while trying frantically to escape. The mother cats were slumped over, listening to their kittens dying cries as they themselves were suffocated.
The person responsible for removing their bodies would have to pry their jaws open to get them off the wire. Cats being gassed do not just fall peacefully asleep, as some pound operators who continue to use gas will tell you.