Your husband disappears to the basement for hours on end, "experimenting" I wouldn't blame you for being suspicious. But hey, don't worry, he's just messing with animals.
Andre is experimenting on himself with matter transference when a fly accidentally gets stuck in the machine with him, turning his head and left hand in to that of a fly's. I do hope he is not left handed. The reveal is wonderful and the head really is quite grotesque. At first he keeps his head covered with a sheet and his hand in his pocket so as not to freak the wife out. He can't speak so he has to type instructions to Helene on his typewriter with his "good hand". The first things he asks for are a glass of milk and a brandy. Who'd of thought! Andre types that he is finding it hard to keep his human mind in control. I don't know how any of it can be human; his head is a freaking great big fly's head! Anyway...
Helene now must find the fly, which has the head of her husband on it by the way, to have any chance of swapping everything back! She enlists the help of their son, shouting at him when he fails to find the fly in their 20 acre garden, geez. Too much time has passed and now Andre is starting to freak out. Unable to fight it any longer, he begs Helene to kill him under this massive press they happen to have in their house. Don't ask.
I love the scene the morning after she squishes him, waking up in bed with a huge smile on her face. Basically, "my husband and father to my child turned in to a monster with a fly head, now he's dead, who gives a fuck?" (Not an actual quote, you understand). Made of tough stuff these broads.
Inspector Charas: He put his head and arm under the press. Why?
Helene: I cannot answer that question; coffee, Inspector?