Just after the doctor started the post mortem on that little girl, the front of his gown is covered with blood. Yet, a few seconds later, after the two other guys appeared, his gown looks better, with less blood. And during the whole post mortem scene, the blood spot actually changes its size a few times.
The film had a notoriously troubled production, with several writers and directors dropping out of the project during development. With a looming release date, sets were built and a crew was assembled before a script was even settled on, and the final draft had to be written around the sets that had already been built. David Fincher, then a popular music video and commercial director, was chosen to helm the film, but he had nonstop creative difficulties with the producers and studios. He has since gone on to disown the film, as he feels it isn't reflective of his vision.