Revealing mistake: When Tomie's head is cut off and her body falls into the wheelchair, look closely - it's clear her body is just a painted mannequin. The skin has a plastic-y sheen to it, and the body itself is entirely too stiff and rigid.
Revealing mistake: When Tomie's disembodied head is on the ground, taunting the lead characters, you can easily tell that the actress is just sticking her head through a hole in the ground. She's moving far too much, which gives away the effect.