Like several Hammers, this has a colonial theme with a misunderstanding in a far corner of the Empire brought home with horrific goings-on in rural England. Down in Cornwall, Jacqueline Pearce suffers under a curse, which turns her periodically into a striking, venomous snake-woman whose bite causes frothing death.
Pearce gives a haunting performance and has a moving death scene, while Willman a substitute for Peter Gushing is also interesting as the monster's tormented but repressed father, Dad's Army's John Laurie is the local loon. It makes a change for an animal bite not to lead to the emergence of a superhero, so the plot comes as a welcome diversion from most films of their ilk.