Towards the end, after arriving back home from the hospital, Beth enters and turns on the light near the front door on Beth's left side. A split second later, the set lighting comes on Beth's right side.
When Beth is in the crawl space under the hospital, she holds her flashlight sideways, casting light on the wall on her left. When they cut to show what she sees as she is crawling, the beam of light is cast in front of her. The scene cuts back and forth between the 2 views, making the mistake very visible.
At the end, Jack Andrews leans in towards the peephole before he is stabbed in the left eye. When he is lying on the ground right after, his right eye is hidden, but his left eye is completely untouched.