Blood Oozes From Dead Woman's Mouth in Greenhouse

by Barry
(Chicago, Illinois, USA)

I believe this artsy thriller film is from the late 60's to mid 70's, and the scene that stands out for me is where a young woman goes into a greenhouse for some reason (either to look for someone, or she hears something, or she just might be tending to plants inside the greenhouse) and a creature kills her with a quick stab. She falls to the ground and blood starts coming out of her mouth.

The odd part of this is that I'm pretty sure the film is in black-and-white with a few scenes in color - like the blood dripping from her mouth. Scenes suddenly switch back and forth.

Sorry I can't remember more, but if anyone has any ideas I would greatly appreciate your sharing!