Since the murder sequence was shot on black-and-white film, the crew decided to use Hersey's syrup instead of fake blood. This chocolate syrup looked just like blood on film and didn't stain. Plus, the cleanup was much sweeter.
The female voice heard yelling at The Owner during the murder sequence isn't actress Diane Mohan. It's Lola McVey, actor Rick McVey's wife in real life.
The basement sequence was entirely improvised on the day of filming. In the original script, Jackson was supposed the find the bloody T-shirt in a closet. However, director Elias Gandy completely rewrote the scene to fit the creepy basement after arriving on location.