The knife stabbed into Eva's back has its blade tip emerge through her left nipple. When Eva's corpse is later shown hanging in Inga's wardrobe, her left nipple is untouched and the blade tip is protruding from her lower sternum.
(at around 38 mins) Angela is wearing a gray nightshirt when she finds Eva dead on her bed and immediately runs screaming out of the bungalow at which point Angela is suddenly wearing a sweater with a colorful forest pattern instead of the nightshirt.
When Angela approaches Inga which is supposedly lying in her bed,
her mouth is closed, but once Angela removes the covers, Inga's decapitated head has open mouth.
When Manuela kills Alvaro, she holds the chainsaw vertically, but wound is being inflicted horizontally.
(spoilers) When Inga is decapitated by the circular saw, an obvious plastic head is used...the mannequin (or whatever the head is really attached to) doesn't even face the saw. Inga looks at it from the side of the slab she's tied to whilst screaming, but as soon as the plastic head comes into the scene, the head faces upwards rather than left or right.
Dead girl hanging from the ceiling is moving her eyes.
Obvious fake stomach when girl is killed at the start of the movie.
When burnt and dead countess is seen, she is obviously wearing a mask, because her eyes move and look healthy behind obvious mask.
When the girls are stalking their female friend who is pretending to have sex, one of them tries to open the door, pretending it's locked, but it can be seen opening before cut to another shot.