Reazione a Catena (also known as Bay of Blood, Twitch of the Death Nerve, Ecologia del Delitto...) is a 1971 horror film by Mario Bava. Designed as a comeback film after he lost his distribution deal with American International Pictures, Bava effectively created a film that has served as the blueprint for the Bodycount/Slasher genre of horror, with many of its sequences copied by other horror films (most notably Friday the 13th and Friday the 13th Part 2).
The film's plot is a convoluted "Who Done It", as people begin dying left and right during the course of a long weekend at the lakeside home of an elderly heiress. There are multiple murderers at work, as a slew of shady characters (and a quartet of sex-obsessed teens) end up dying in horrific fashion. There is also a surprise ending that will shock you...
This film provides examples of:
- Anyone Can Die: And does.
- Asshole Victim: Pretty much everyone who dies except for the heiress, the teenagers, and possibly the entomologist and his wife.
- Big Bad Ensemble: Simon, Renata, Albert, Frank, and Laura are all the killers in the main plot, while Count Donati kickstarts the plot by killing his wife in the prologue (then promptly being offed himself).
- Don't Go in the Woods: Or swimming in the bay. Or in the cabin nearby. Or... anywhere, really. Just drive away.
- Death by Sex: Two kids. Impaled. But in this one the girl is on top.
- Eldritch Location: Similar to other offerings in the genre that the film helped inspire, the bay and its environs seem to have a malevolent, murderous influence on people, though this falls into the Maybe Magic, Maybe Mundane category.
- Extremely Short Timespan: The majority of the action unfolds over a single day. It is not clear how much time elapses between the Contessa's death and the start of the main action, but it does not seem to be more than a few days.
- Gardening-Variety Weapon: Simon uses a billhook as his primary weapon for murdering people.
- Gorn: Comfortably Bava's goriest film which sickened audiences back in the day but is now seen as the forefather of the slasher genre.
- Gory Discretion Shot: Averted. The kills are lovingly photographed in detail.
- Greed: The underlying motivation which kills literally.
- HeelFace Door-Slam: After Simon kills the secretary for the death of his mother, the heiress, it's revealed that he killed all the teenagers for finding Donati's body and made a deal to sell the bay in order to keep it a secret. He seems to show some remorse for his part in all this but is immediately killed by Albert.
- Hooks and Crooks: One character gets killed when a billhook catches her throat.
- I Just Shot Marvin in the Face: Renata and Albert end up being killed when their son shoots them with a double-barreled shotgun, without realizing that they are dead for real.
- Impaled with Extreme Prejudice: The two boffing kids and Simon.
- Kill 'Em All: Barring the children, everyone is dead at the end.
- The Killer Becomes the Killed: The Count, Simon, Frank and his lover, and the greedy parents in the finale.
- Mind Screw: The ending. And most of the movie.
- Peek-a-Boo Corpse:
- Youth Is Wasted on the Dumb: Some can say this of the four young people who stop for a quick death.