[voerioc]

On one French nuclear test footage, we can clearly see a bad FX at 0.40 sec.

https://www.youtube.com/watch?v=yDtHowdjOKs

It's on the bottom left. You can see the cloud disappearing on its border, as if it had been erased manually. If it had been erased by the blow of an atomic bomb, it would have been blown away like when you blow on the could of smoke of a cigarette, in a chaotic way.