The opening scene shows the murder scene, following Emily's bloody footprints from the kitchen to the bedroom. Later in the film, when the stabbing is depicted, Emily walks toward the bed leaving no footprints, and the camera shows a clear shot of her feet which have no blood on them.
The goof item below may give away important plot points.
When Emily kills her husband, she is seemingly in a sleepwalking trance. The movie later reveals that she faked the sleepwalking in order to set up a NGRI legal defense. Even with that in mind, there is no reason for her to fake sleepwalking while in the act of killing her husband. He's beyond a point where he would be testifying about anything. So why continue with the charade? Apparently to fool the movie audience about the authenticity of her sleepwalking.