The original 1958 version of The Fly starts with a wife crushing her husband’s head in a mechanical press and is told in flashback from there.
The 1986 David Cronenberg version is better known today, but the concept is essentially the same: an over-dedicated scientist attempts to teleport himself, only unknown to him a fly also gets into his machine, and their molecules get combined. In Cronenberg’s version, the scientists slowly transforms into a fly, in the original the creature’s head and arm gets swapped.
Its a fairly gross premise, and there is pathos too in the ending, as the scientist’s brother (Vincent Price), having tried to capture the half-man half-fly version with the human head, enacts a mercy killing to prevent him being eaten by a spider!
This great graphic poster is a rare French 120x80cm from a 1970s re-release. It is for sale here.