“What was so amazing,” said Weisberg, “was anybody in the poison gas community would immediately know that this was total bullshit – such obvious bullshit.”

In the movie, poison gas is contained in these little green glass spheres connected together like a string of pearls, basically because it looks cool and because fragile glass spheres full of poison gas are exciting. They really milked it in the movie.

“Unfortunately chemical weapons are very boring because essentially they’re a two-chamber cell with two odourless and colourless gases in each chamber. When the shell is detonated, the gases mix and become the [nerve agent] VX.

“There was no way to do that [realistically] on the screen with any kind of excitement. In real life it’s all invisible and boring, as per usual. So we invented this string-of-pearls approach to have these little globes with green gases in them, to give visual interest and to create jeopardy. If one of these globules broke you’d be in real trouble.”

In real life, chemical weapons look nothing like that.