Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This movie was released as The Bloody Dead in the USA with some added scenes. It's a mystery thriller in a genre I hadn't heard of before seeing it - a Krimi, a style of German movie made mostly in the 60s, which have some similarities to the Italian Giallo films and seem to be mostly based on books by Edgar Wallace, as this one was.
Klaus Kinski plays a man sentenced to life in an insane asylum for murder, but after the first part of the film we hardly see him. He has a twin brother, but it takes us a while to figure out which one is the evil twin. The blue hand of the title is a blue steel hand with knives for fingers from an old suit of armor. Freddie Kruger would envy it, but really it's a pretty lame murder weapon. The movie is fairly predictable with lots of murders and suspects, a Scotland Yard inspector, suspicious family members, brutal henchmen in white lab coats, a big spooky mansion full of old suits of armor, and an evil insane asylum doctor with a monacle - Dr. Mangrove. He wants to punish a nurse at his asylum for snooping on him, so he pulls back a picture on the wall but instead of the usual safe in the wall there's a glass tank holding a Boa Constrictor. He puts it around the nurse's neck and then holds its head up to her face. She screams, so we can assume she died, but I don't know if she was killed from the bite or the choking. There is a cell at the asylum called Cell 9. A young woman prisoner is thrown into Cell 9 because she refuses to cooperate with Dr. Mangrove. When she is thrown in, there is a cage on the floor full of rats. Then two ramps open up on a wall and lots of Boa Constrictors along with a Burmese Python are dumped into the room. They crawl around on the floor terrifying the woman, who doesn't realize they're so slow they could never catch her and that they're harmless. But we're supposed to think that because they're snakes they are horribly deadly. Fortunately she is rescued before one of the mild-mannered constrictors can strangle her to death or something.